Spinal Disc Prosthesis and Associated Methods

ABSTRACT

A prosthetic device for insertion into a spondylosed intervertebral space is provided. The prosthetic device includes a first component having a first flange for longitudinally engaging a first vertebra during longitudinal insertion therein, and a second component having a second flange for longitudinally engaging a second vertebra during longitudinal insertion therein. One of the first and second components comprises a projection and the other of the first and second components comprises a recess, the projection and recess being adapted to engage one another. One of the projection and the recess are offset relative to the other of the projection and the recess to accommodate the spondylosed relationship between the first and second vertebrae.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/446,963 filed on Feb. 12, 2003. U.S. Provisional Application No.60/446,963 is herein incorporated by reference for all legitimatepurposes.

BACKGROUND

The present disclosure relates generally to the field of orthopedics andspinal surgery, and in some embodiments, the present disclosure relatesto intervertebral prosthetic joints for use in the total or partialreplacement of a natural intervertebral disc, and methods and tools foruse therewith.

In the treatment of diseases, injuries or malformations affecting spinalmotion segments, and especially those affecting disc tissue, it has longbeen known to remove some or all of a degenerated, ruptured or otherwisefailing disc. In cases involving intervertebral disc tissue that hasbeen removed or is otherwise absent from a spinal motion segment,corrective measures are taken to ensure the proper spacing of thevertebrae formerly separated by the removed disc tissue.

In some instances, the two adjacent vertebrae are fused together usingtransplanted bone tissue, an artificial fusion component, or othercompositions or devices. Spinal fusion procedures, however, have raisedconcerns in the medical community that the bio-mechanical rigidity ofintervertebral fusion may predispose neighboring spinal motion segmentsto rapid deterioration. More specifically, unlike a naturalintervertebral disc, spinal fusion prevents the fused vertebrae frompivoting and rotating with respect to one another. Such lack of mobilitytends to increase stresses on adjacent spinal motion segments.

Additionally, several conditions may develop within adjacent spinalmotion segments, including disc degeneration, disc herniation,instability, spinal stenosis, spondylosis and facet joint arthritis.Consequently, many patients may require additional disc removal and/oranother type of surgical procedure as a result of spinal fusion.Alternatives to spinal fusion are therefore desirable.

In particular, this disclosure relates to an articulating discprosthesis that can be inserted from the anterior approach to aid in thecorrection of spondylolisthesis.

SUMMARY

A prosthetic device for longitudinal insertion into an intervertebralspace defined between a pair of spondylosed vertebrae is provided. Theprosthetic device includes a first component, which includes a firstflange longitudinally extending along a first bearing surface, and aprojection extending from a first articular surface, the projectionbeing offset relative to the first articular surface. The prostheticdevice further includes a second component adapted to be engaged withthe first component, the second component including a second flangelongitudinally extending along a second bearing surface, the secondflange being substantially aligned with the first flange upon engagementof the second component with the first component, and a recess formed inthe second articular surface, the recess being offset relative to thesecond articular surface thereby accommodating a spondylosedrelationship between a first vertebra and a second vertebra adjacent tothe first vertebra. The projection and the recess engage one another toprovide for articulating motion between the first and second components.

In another embodiment, a prosthetic device for insertion into anintervertebral space is provided. The prosthetic device includes a firstcomponent having a means for longitudinally engaging a first vertebraduring longitudinal insertion therein, and a second component having ameans for longitudinally engaging a second vertebra during longitudinalinsertion therein, wherein one of the first and second componentscomprises a projection and the other of the first and second componentscomprises a recess, the projection and recess being adapted to engageone another. One of the projection and the recess is offset relative tothe other of the projection and the recess.

In yet another embodiment, an arrangement for stabilizing a portion of aspondylosed spinal column is provided. The arrangement includes aprosthetic articulating device adapted to engage adjacent spondylosedvertebral bodies, the prosthetic articulating device including a firstcomponent and an offset second component, the first and secondcomponents cooperating to permit articulating motion between the firstand second components. The arrangement further includes an artificialligament disposed adjacent to the prosthetic articulating device whereinthe artificial ligament engages each of the vertebral bodies.

In yet another embodiment, a method for correcting spondylolisthesisfrom an anterior approach is provided. The method includes providing aprosthetic device having a first articular component with an offsetprojection, and a second articular with an offset recess adapted toengage with the offset projection, and longitudinally inserting thefirst articular component into a first vertebra and longitudinallyinserting the second articular component into a second vertebra, thesecond vertebra being adjacent to the first vertebra.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a lateral view of a portion of a spondylosed vertebral column.

FIG. 2 is a lateral view of a pair of adjacent vertebral endplates ofFIG. 1.

FIG. 3 a is a lateral view of the pair of adjacent vertebral endplatesof FIG. 2 with a rod and screw arrangement.

FIG. 3 b is a longitudinal, partial sectional view of the pair ofadjacent vertebral bodies of FIG. 3 a.

FIG. 4 a is an isometric view of an articulating prosthetic joint forlateral insertion according to one embodiment of the present disclosure.

FIG. 4 b is an isometric view of an articulating prosthetic joint forlateral insertion according to another embodiment of the presentdisclosure.

FIG. 4 c is a front view of the articulating prosthetic joint forlateral insertion of FIG. 4 b.

FIG. 5 is a longitudinal view of the prosthetic joint of FIG. 4 a.

FIG. 6 is a lateral view of the prosthetic joint of FIG. 4 a.

FIG. 7 is a lateral, partial sectional view of the prosthetic joint ofFIG. 4 a disposed between a pair of spondylosed vertebral endplates.

FIG. 8 is a lateral, partial sectional view of an alternativearticulating prosthetic joint disposed between a pair of vertebralendplates.

FIG. 9 is an isometric view of an alternative articulating prostheticjoint according to another embodiment of the present disclosure.

FIG. 10 is a lateral, partial sectional view of the prosthetic joint ofFIG. 9 disposed between a pair of spondylosed vertebral endplates.

FIG. 11 is a lateral, partial sectional view of an alternativearticulating prosthetic joint disposed between a pair of vertebralendplates.

FIG. 12 is an isometric view of a disc prosthesis according to anotherembodiment of the present disclosure.

FIG. 13 is an isometric view of an alternative disc prosthesis accordingto another embodiment of the present disclosure.

FIG. 14 is an isometric view of an alternative articulating prostheticjoint for anterior insertion according to another embodiment of thepresent disclosure.

FIG. 15 is a longitudinal view of the prosthetic joint of FIG. 14.

FIG. 16 is a lateral view of the prosthetic joint of FIG. 14.

FIG. 17 is a lateral view of the prosthetic joint of FIG. 14 disposedbetween a pair of spondylosed vertebral endplates.

FIG. 18 is a longitudinal view of an alternative articulating prostheticjoint for anterior insertion according to another embodiment of thepresent disclosure.

FIG. 19 is a longitudinal view of an alternative articulating prostheticjoint for anterior insertion according to yet another embodiment of thepresent disclosure.

FIG. 20 is a longitudinal view of an alternative articulating prostheticjoint for anterior insertion according to yet another embodiment of thepresent disclosure.

FIG. 21 is a longitudinal view of a pair of vertebral endplates havingslots for receiving the prosthetic joint of FIG. 18.

FIG. 22 is a longitudinal view of a pair of vertebral endplates havingslots for receiving the prosthetic joint of FIG. 19.

FIG. 23 is a longitudinal view of a pair of vertebral endplates havingslots for receiving the Prosthetic joint of FIG. 20.

FIG. 24 is a lateral, partial sectional view of the prosthetic joint ofFIG. 14 disposed between a pair of spondylosed vertebral endplates andan orthopedic implant.

FIG. 25 is a lateral, partial sectional view of the prosthetic joint ofFIG. 14 disposed between a pair of spondylosed vertebral endplates and alag screw.

FIG. 26 is a schematic top view of the arrangement depicted in FIG. 25.

FIG. 27 is a schematic top view of a vertebral body depicting a path fortransforaminal insertion.

FIG. 28 is an isometric view of an alternative articulating prostheticjoint for transforaminal insertion according to another embodiment ofthe present disclosure.

FIG. 29 is a lateral view of the prosthetic joint of FIG. 28.

FIG. 30 is a longitudinal view of the prosthetic joint of FIG. 28.

FIG. 31 a is a lateral, partial sectional view of the prosthetic jointof FIG. 28 disposed between a pair of vertebral endplates.

FIG. 31 b is a longitudinal, partial sectional view of the prostheticjoint of FIG. 28 disposed between a pair of vertebral endplates.

FIG. 32 is a schematic top view depicting a transforaminal slot formedin a vertebral endplate.

FIG. 33 is a schematic top view depicting a milling apparatus showninserted above a vertebral endplate.

FIG. 34 a is a lateral view of the milling apparatus of FIG. 33 showndisposed between a pair of adjacent vertebral endplates.

FIG. 34 b is a detailed view of a milling tool of the milling apparatusof FIG. 34 a.

FIG. 34 c is a detailed view of an alternative milling tool.

FIG. 35 is a schematic view of the milling apparatus of FIG. 33.

FIG. 36 is an isometric view of in alternative articulating prostheticjoint for transforaminal insertion according to another embodiment ofthe present disclosure.

FIG. 37 is a lateral view of the prosthetic joint of FIG. 36.

FIG. 38 is a longitudinal view of the prosthetic joint FIG. 36.

FIG. 39 is an isometric view of an alternative articulating prostheticjoint for anterior-oblique insertion according to another embodiment ofthe present disclosure.

FIG. 40 is a longitudinal view of the prosthetic joint of FIG. 39.

FIG. 41 is a lateral view of the prosthetic joint of FIG. 39.

FIG. 42 is lateral, partial sectional view of the prosthetic joint ofFIG. 39 disposed between a pair of vertebral endplates.

FIG. 43 is a longitudinal, partial sectional view of the prostheticjoint of FIG. 39 disposed between a pair of vertebral endplates.

FIG. 44 a is a top, schematic view depicting a slot formed in avertebral endplate for receiving the prosthetic joint of FIG. 39.

FIG. 44 b is a schematic view depicting an alignment process associatedwith the insertion of the prosthetic joint of FIG. 39.

FIG. 45 is an exploded view an alternative prosthetic joint according toyet another embodiment of the present disclosure.

FIG. 46 is an isometric view of the prosthetic joint of FIG. 45.

FIG. 47 is a longitudinal view of the prosthetic joint of FIG. 46.

FIG. 48 is a longitudinal view of a pair of adjacent vertebralendplates.

FIG. 49 a is a plan view of an articular component of the prostheticjoint of FIG. 45.

FIG. 49 b is a sectional view of the articular component of FIG. 49 ataken along the line-49 b-49 b.

FIG. 50 a is a plan view of a modular projection member of theprosthetic joint of FIG. 45.

FIG. 50 b is a sectional view of the modular projection member of FIG.50 a taken along the line 50 b-50 b.

FIG. 51 is a plan view of the modular projection member of FIG. 50 ainserted into the articular component of FIG. 49 a.

FIG. 52 is a plan view of the modular projection member of FIG. 50 ainserted into the articular component of FIG. 49 a depicting the modularprojection member in a different position relative to FIG. 51.

DESCRIPTION

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments, or examples,illustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended. Any alterations andfurther modifications in the described embodiments, and any furtherapplications of the principles of the invention as described herein arecontemplated as would normally occur to one skilled in the art to whichthe invention relates. As such, individual features of separatelydescribed embodiments can be combined to form additional embodiments. Inaddition, examples of deformities such as spondylolisthesis arediscussed; however, it is understood that the various prosthetic devicesdescribed herein can be adapted for use between not only spondylosedvertebrae, but substantially aligned vertebrae as well.

I. Lateral Correction

In many cases of deformity, such as spondylolisthesis, one or morevertebral bodies can be displaced with respect to other vertebrae or thesacrum. In such a deformity, it is desirable to reduce the extent ofdisplacement, by re-positioning the displaced bodies from their previousposition. A spondylolisthesis reduction can be a technically demandingprocedure requiring great care to prevent neurological impairment anddamage to surrounding soft tissue.

Referring now to FIG. 1, shown therein is a lateral view of a portion ofa spinal column 10, illustrating a group of adjacent upper and lowervertebrae V1, V2, V3, V4 separated by natural intervertebral discs D1,D2, D3. The illustration of four vertebrae is only intended as anexample. Another example would be a sacrum and one vertebrae.

As shown in the drawing, the vertebrae V2 is dislocated from thevertebrae V1 in a direction shown by arrow 22. Likewise, vertebrae V3 isdislocated in a direction shown by arrow 23 and vertebrae V4 isdislocated in a direction shown by arrow direction 24. It is desiredthat the position of vertebrae V2, V3, V4 be corrected by moving them ina direction opposite to the arrows 22, 23, 24, respectively.

Referring now to FIG. 2, for the sake of further example, two of thedisplaced vertebrae will be discussed, designated as the lower vertebraeV_(L) and the upper vertebrae V_(U). In one embodiment, some or all ofthe natural disc that would have been positioned between the twovertebrae V_(L), V_(U) is typically removed via a discectomy or asimilar surgical procedure, the details of which would be known to oneof ordinary skill in the art. Removal of the diseased or degenerateddisc results in the formation of an intervertebral space S between theupper and lower vertebrae V_(U), V_(L).

In the present embodiment, it is desired to insert a prosthetic jointinto the intervertebral space S, similar to the prosthetic jointdisclosed in U.S. Ser. No. 10/042,589 filed Jan. 9, 2002, which isincorporated by reference. However, certain changes are required of theabove-referenced prosthetic joint. For the following description, theprosthetic joints discussed and described can be identical to thosedisclosed in the above-referenced patent application, with theexceptions discussed and suggested below.

Spondylolisthesis has not heretofore been corrected from the lateralsurgical approach. However, in some instances, correction ofspondylolisthesis may be desirable from a lateral approach due to thepresence of vessels and/or the nervous plexus. In some embodiments, thelateral approach may be particularly pertinent when correctingspondylolisthesis in the lumbar region of the spine, although it will beunderstood that other regions of the spine are also contemplated.

Referring to FIGS. 3 a and 3 b, correction of spondylolisthesis can beaddressed from a lateral approach by, for example, providing a pair ofbone screws 30, 32 for insertion into the vertebrae V_(U), V_(L),respectively. In one embodiment, the bone screws 30, 32 are bi-cortical.However, it is understood that the bone screws may alternatively beuni-cortical. Moreover, the bone screws 30, 32 may be formed of avariety of materials such as any resorbable material, titanium, andPEEK. The PEEK embodiment is advantageous due to the radiotranslucentproperties resulting from the use of PEEK material. It is furtherunderstood that the bone screws 30, 32 may alternatively be of any othermechanical structure, and as such, may take the form of pins or rivets,for example. Moreover, the bone screws 30, 32 are not limited to havingthreaded portions to engage the vertebrae V_(U), V_(L).

The bone screws 30, 32 may be linked to one another via a rod 34, whichis configured to rotate about both of the bone screws. It is understoodthat a variety of connecting members may be used other than the rod 34.For example, a non-uniform linkage member may be used to link the bonescrews 30, 32. A non-uniform linkage member may provide a plurality ofslots and/or grooves that can be engaged in order to aid in its rotationabout the bone screws. The rod 34 may be connected prior to insertion ofthe bone screws 30, 32 into the vertebrae V_(U), V_(L), oralternatively, may be subsequently connected after placement of thescrews. By applying a rotating force to the rod 34 in the direction ofarrow 36, the upper vertebra V_(U) is encouraged back into a desiredposition relative to the lower vertebra V_(L). The rotating force can beapplied, for example, by a rotatable wrench (not shown) that can be usedby a surgeon. It is understood that the upper vertebra V_(U) may notreach entirely to a fully corrected position in relation to the lowervertebra V_(L), but the displacement can at least be reduced.

Although not depicted, in another embodiment, it is contemplated thatthe spondylosed vertebrae V_(U), V_(L) can be addressed from bothlateral directions. Thus, a pair of bone screws substantially identicalto the bone screws 30, 32 may be inserted into the vertebrae V_(U),V_(L) on the opposite side from and in the opposite direction to thebone screws 30, 32. In such an arrangement, the rod 34 can be replacedwith a ratcheting system that engages each of the bone screw pairs, andas such, the vertebrae V_(U), V_(L) can be rotated relative to oneanother to encourage the vertebrae into a desired position relative toone another.

Still further, the rod 34 may include any number and type of engagementmeans to receive any number and type of rotating tools used by asurgeon. For example, a keyed connection may provide more stability whenengaging the rod 34 with a corresponding rotating tool. In otherexamples, a clamping tool may be used and corresponding clamping notchesmay be formed in the rod 34 to receive the clamping tool. Such anarrangement may aid in achieving the force necessary for rotation.

Moreover, additional rods 34 and bone screws 30, 32 are contemplated foruse in rotating the spondylosed vertebrae V_(U), V_(L) back into adesired position relative to one another. Additional rods 34 and bonescrews 30, 32 may provide additional stability during the procedure.

Furthermore, although depicted as a substantially lateral insertion, theinsertion of the bone screws 30, 32 into the vertebrae V_(U), V_(L) canbe slightly angled relative to the lateral direction. Such angling ofthe bone screws 30, 32 during insertion may provide a preferred grippingangle from which the surgeon can begin rotation of the vertebrae V_(U),V_(L) relative to one another.

Referring to FIGS. 4 a, 5, and 6, shown therein is one embodiment of anoffset intervertebral articulating prosthetic joint 40 for insertioninto the intervertebral space S (FIG. 2) to aid in the correction ofspondylolisthesis. The articulating prosthetic joint 40 extendsgenerally along a longitudinal axis L and includes a first articularcomponent 42 and a second articular component 44. The articularcomponents 42, 44 cooperate to form the prosthetic joint 40 which issized and configured for disposition within the intervertebral space S(FIG. 2) between adjacent vertebral bodies V_(U), V_(L) (FIG. 2).

The prosthetic joint 40 provides relative pivotal and rotationalmovement between the adjacent vertebral bodies to maintain or restoremotion substantially similar to the normal bio-mechanical motionprovided by a natural intervertebral disc. More specifically, thearticular components 42, 44 are permitted to pivot relative to oneanother about a number of axes, including lateral or side-to-sidepivotal movement about longitudinal axis L and anterior-posteriorpivotal movement about a transverse axis T. It should be understood thatin one embodiment of the disclosure, the articular components 42, 44 arepermitted to pivot relative to one another about any axes that lies in aplane that intersects longitudinal axis L and transverse axis T.

Furthermore, the articular components 42, 44 are permitted to rotaterelative to one another about a rotational axis R. Although theprosthetic joint 40 has been illustrated and described as providing aspecific combination of articulating motion, it should be understoodthat other combinations of articulating movement are also possible, suchas, for example, relative translational or linear motion, and suchmovement is contemplated as falling within the scope of the presentdisclosure.

Although the articular components 42, 44 of prosthetic joint 40 may beformed from a wide variety of materials, in one embodiment of thedisclosure, the articular components 42, 44 are formed of acobalt-chrome-molybdenum metallic alloy (ASTM F-799 or F-75). However,in alternative embodiments of the disclosure, the articular components42, 44 may be formed of other materials such as titanium or stainlesssteel, a polymeric material such as polyethylene, or any otherbiocompatible material that would be apparent to one of ordinary skillin the art.

The articular components 42, 44 each include a bearing surface 46, 48,respectively, that may be positioned in direct contact with vertebralbone and is preferably coated with a bone-growth promoting substance,such as, for example, a hydroxyapatite coating formed of calciumphosphate. Additionally, the bearing surfaces 46, 48 of the articularcomponents 42, 44, respectively, may be roughened prior to being coatedwith the bone-growth promoting substance to further enhance boneon-growth. Such surface roughening may be accomplished by way of, forexample, acid etching, knurling, application of a bead coating, or othermethods of roughening that would occur to one of ordinary skill in theart.

Articular component 42 includes a support plate 50 having an articularsurface 52 and the opposite bearing surface 46. Support plate 50 issized and shaped to substantially correspond to the size and shape of avertebral endplate of the adjacent vertebral body V_(L) (FIG. 2). Thesupport plate 50 may include one or more notches 54 or other types ofindicia for receiving or engaging with a corresponding portion of asurgical instrument (not shown) to aid in the manipulation and insertionof the prosthetic joint 40 within the intervertebral space S (FIG. 2)between the adjacent vertebral bodies V_(U), V_(L) (FIG. 2). Thesurgical instrument (not shown) is preferably configured to hold thearticular components 42, 44 at a predetermined, orientation and spatialrelationship relative to one another during manipulation and insertionof the prosthetic joint 40, and to release the articular components 42,44 once properly positioned between the adjacent vertebrae.

In one embodiment of the disclosure, the articular component 42 includesa projection 56 having a convex shape, which may be configured as aspherical-shaped ball (half of which is shown). It should be understoodthat other configurations of the projection 56 are also contemplated,such as, for example, cylindrical, elliptical or other arcuateconfigurations or possibly non-arcuate configurations. It should also beunderstood that the remaining portion of articular component 42 may takeon planar or non-planar configurations, such as, for example, an angularor conical configuration extending about the projection 56.

A flange member or keel 58 extends from the bearing surface 46 and isconfigured for disposition within a preformed opening in the adjacentvertebral endplate. As with the bearing surface 46, the keel 58 may becoated with a bone-growth promoting substance, such as, for example, ahydroxyapatite coating formed of calcium phosphate. Additionally, thekeel 58 may be roughened prior to being coated with the bone-growthpromoting substance to further enhance bone on-growth. In oneembodiment, the keel 58 extends along the transverse axis T and issubstantially centered along the bearing surface 46. However, it shouldbe understood that other positions and orientations of the keel 58 arealso contemplated.

In one embodiment, the keel 58 transversely extends along a substantialportion of the articular component 42. Such an embodiment wouldaccommodate insertion of the prosthetic joint 40 using a lateralapproach as opposed to, for example, an anterior approach. In a furtherembodiment, the keel 58 may be angled, tapered, or configured in someother shape to facilitate the functional demands of the keel. In stillanother embodiment, the keel 58 may be configured as a winged keel,including a lateral portion (not shown) extending across the main bodyportion of keel 58.

In one embodiment, the keel 58 includes three openings 60 extendingtherethrough to facilitate bone through-growth to enhance fixation tothe adjacent vertebral bodies V_(U), V_(L), (FIG. 2). However, it shouldbe understood that any number of openings 60 may be defined through thekeel 58, including a single opening or two or more openings. It shouldalso be understood that the openings 60 need not necessarily extendentirely through the keel 58, but may alternatively extend partiallytherethrough. It should further be understood that the keel 58 need notnecessarily define any openings 60 extending either partially orentirely therethrough. Additionally, although the openings 60 areillustrated as having a circular configuration, it should be understoodthat other sizes and configurations of openings 60 are alsocontemplated.

In one embodiment, the articular component 44 includes a support plate70 having an articular surface 72 and the opposite bearing surface 48.Support plate 70 may be sized and shaped to substantially correspond tothe size and shape of a vertebral endplate of the adjacent vertebralbody V_(U). The support plate 70 may include one or more notches 74 orother types of indicia for receiving and engaging with a correspondingportion of a surgical instrument, such as discussed above with referenceto articular component 42.

In one embodiment, the articular surface 72 includes a recess 76. In oneembodiment, the recess 76 has a concave shape, and is configured as aspherical-shaped socket. However, it should be understood that otherconfigurations of the recess 76 are also contemplated, such as, forexample, cylindrical, elliptical or other arcuate configurations orpossibly non-arcuate configurations. The remaining portion of thearticular surface 72 can be angled or otherwise configured to facilitatethe insertion and/or use of the prosthesis.

Although the concave recess 76 is illustrated as having a generallysmooth, uninterrupted articular surface, it should be understood that asurface depression or cavity may be defined along a portion of therecess 76 to provide a means for clearing out matter, such asparticulate debris, that is disposed between the abutting articularcomponents 42, 44. In such case, the convex articular surface of theprojection 56 may alternatively define a generally smooth, uninterruptedarticular surface. In another embodiment, each of the convex projection56 and the concave recess 76 may define a surface depression tofacilitate removal of particulate matter disposed between the abuttingarticular components 42, 44.

A flange member, or keel 68, configured similar to the keel 58 ofarticular component 42, extends from the bearing surface 48. In oneembodiment, the keel 68 extends along the transverse axis T and isoffset from the center of the bearing surface 48. Such an embodimentwould accommodate insertion of the prosthetic joint 40 using a lateralapproach. However, it should be understood that other shapes, positionsand orientations of the keel 68 are also contemplated. For example, inFIGS. 4 b and 4 c, the keels 58 and 68 may be angled relative to thetransverse axis T to aid in the circumvention of veins, arteries, bonyportions, or other obstacles that may be in place during insertion ofthe prosthetic joint 40. Also, the keel 68 may be angled, tapered, orconfigured in some other shape to facilitate the functional demands ofthe keel. In still another embodiment, the keel 68 may be configured asa winged keel, including a transverse portion extending across the mainbody portion of the keel 68.

In one embodiment, and referring to FIG. 5; the keel 68 also includesthree openings 70 extending therethrough to facilitate bonethrough-growth to enhance fixation to the adjacent vertebra. However, itshould be understood that any number of openings 70 may be definedthrough keel 70, including a single opening or two or more openings. Itshould also be understood that the openings 70 need not necessarilyextend entirely through the keel 68, but may alternatively extendpartially therethrough. It should further be understood that the keel 68need not necessarily define any openings 70 extending either partiallyor entirely therethrough. Additionally, although the openings 70 areillustrated as having a circular configuration, it should be understoodthat other sizes and configurations of openings 70 are alsocontemplated. As discussed above, the bearing surfaces 46, 48 that arein direct contact with vertebral bone are preferably coated with abone-growth promoting substance. Specifically, the bearing surface 48and the surface of the keel 68 can be coated with hydroxyapatite topromote bony engagement with the adjacent vertebral body V_(U). As alsodiscussed above, the bearing surface 48 and the surface of keel 68 canbe roughened prior to application of the hydroxyapatite coating.

In some embodiments, one or both of the keels 58, 68 may include a sharpforward edge, illustrated by edge 68 a of FIG. 4. By having such anedge, insertion of the keel into the associated vertebral body isfacilitated. Also, the edge 68 a can be of sufficient sharpness that theadjacent vertebral bodies do not require a slot for receiving the keel68, discussed in greater detail below.

Referring to FIG. 7, to accommodate insertion of the offset prostheticjoint 40 within a spondylosed intervertebral space, the partiallycorrected upper and lower vertebrae V_(U), V_(L) can be prepared toaccept the prosthetic joint 40 (shown in section in FIG. 7 a)therebetween. Specifically, elongate openings or slots 80, 82 may beformed along the vertebral endplates of the upper and lower vertebraeV_(L), V_(U), respectively, at a predetermined width and to apredetermined depth. The slots 80, 82 can be laterally offset from eachother to accommodate the displaced vertebrae V_(L) and/or V_(U). In oneembodiment, the elongate slots 80, 82 are rectangular-shaped and extendlaterally through the vertebrae V_(L), V_(U), respectively. In aspecific embodiment, the slots 80, 82 are formed by chiseling orcuretting. However, other methods of forming slots 80, 82 are alsocontemplated as would occur to one of ordinary skill in the art, suchas, for example, by drilling or reaming. Furthermore, for someembodiments of the prosthetic joint 40, the keels 58 and/or 68 can formtheir own corresponding slots 80, 82, respectively.

Referring to FIG. 8, in one embodiment, the upper and lower vertebraeV_(U), V_(L) may be fully corrected, and thus, an alternativearticulating prosthetic joint 90 may be used in correctingspondylolisthesis. The articulating joint 90 may be substantiallysimilar to the prosthetic joint 40 with the exception of the orientationof various elements of the articulating joint 90. For example, toaccommodate insertion into fully corrected upper and lower vertebraeV_(U), V_(L), the articulating joint 90 may include alaterally-extending keel 92 that is substantially centered on an upperarticulating component 94 of the articulating joint and alaterally-extending keel 96 that is substantially centered on a lowerarticulating component 98. Furthermore, the upper articulating component94 may include a recess 100 that is substantially centered to correspondto a substantially centered projection 102 extending from the lowerarticulating component 98. In one embodiment, the upper and lowerarticulating components 94, 98 are substantially flush with one anotherwhen disposed between fully corrected upper and lower vertebrae V_(U),V_(L).

To accommodate insertion of the offset prosthetic joint 90, the fullycorrected upper and lower vertebrae V_(U), V_(L) can be prepared toaccept the prosthetic joint 90 therebetween. Specifically, elongateopenings or slots 104, 106 may be formed along the vertebral endplatesof the upper and lower vertebrae V_(U), V_(L), respectively, at apredetermined width and to a predetermined depth. The slots 104, 106 canbe substantially aligned with each other to accommodate the fullycorrected upper and lower vertebrae V_(U), V_(L). In one embodiment, theelongate slots 104, 106 are rectangular-shaped and extend laterallythrough the vertebrae V_(U), V_(L), respectively. In a specificembodiment, the slots 104, 106 are formed by chiseling or curetting.However, other methods of forming slots 104, 106 are also contemplatedas would occur to one of ordinary skill in the art, such as, forexample, by drilling or reaming. Furthermore, for some embodiments ofthe prosthetic joint, the keels 92 and/or 96 can form their owncorresponding slots 104, 106, respectively.

Referring to FIG. 9, in an alternative embodiment, a slidable prostheticjoint 110 can be used to help with the lateral approach for treatingspondylolisthesis. The sliding joint 110 extends generally along thelongitudinal axis L and includes a first slidable component 112 and asecond slidable component 114. The slidable components 112, 114cooperate to form the sliding joint 110 which is sized and configuredfor disposition within an intervertebral space between adjacentvertebral bodies.

The sliding joint 110 provides movement between the adjacent vertebralbodies to maintain or restore some of the motion similar to the normalbio-mechanical motion provided by a natural intervertebral disc. Morespecifically, the slidable components 112, 114 are permitted totranslate relative to one another in the axial plane.

Although the slidable components 112, 114 of prosthetic joint 110 may beformed from a wide variety of materials, in one embodiment, the slidablecomponents 112, 114 are formed of a cobalt-chrome-molybdenum metallicalloy (ASTM F-799 or F-75). However, in alternative embodiments, theslidable components 112, 114 may be formed of other materials such astitanium or stainless steel, a polymeric material such as polyethylene,or any other biocompatible material that would be apparent to one ofordinary skill in the art. The surfaces of the slidable components 112,114 that are positioned in direct contact with vertebral bone arepreferably coated with a bone-growth promoting substance, such as, forexample, a hydroxyapatite coating formed of calcium phosphate.Additionally, the surface of the slidable components 112, 114 that arepositioned in direct contact with vertebral bone are preferablyroughened prior to being coated with the bone-growth promoting substanceto further enhance bone on-growth. Such surface roughening may beaccomplished by way of, for example, acid etching, knurling, applicationof a bead coating, or other methods of roughening that would occur toone of ordinary skill in the art.

Slidable component 112 includes a support plate 116 having a slidablesurface 118 and an opposite bearing surface 120. Support plate 116 ispreferably sized and shaped to substantially correspond to the size andshape of the vertebral endplate of an adjacent vertebra. The supportplate 116 can include one or more notches 122 or other types of indiciafor receiving and engaging with a corresponding portion of a surgicalinstrument (not shown) to aid in the manipulation and insertion of theprosthetic joint 110 within an intervertebral space between adjacentvertebrae. The surgical instrument (not shown) is preferably configuredto hold the slidable components 112, 114 at a predetermined orientationand spatial relationship relative to one another during manipulation andinsertion of the prosthetic joint 110, and to release the slidablecomponents 112, 114 once properly positioned between the adjacentvertebrae.

A flange member or keel 124 extends from the bearing surface, 120 and isconfigured for disposition within a preformed opening in the adjacentvertebral endplate. In one embodiment, the keel 124 extendsperpendicularly from the bearing surface 120 and is approximatelycentrally located along the bearing surface 120. However, it should beunderstood that other positions and orientations of the keel 124 arealso contemplated.

In one embodiment, the keel 124 transversely extends along a substantialportion of the support plate 114. Such an embodiment would accommodateinsertion of the prosthetic joint 110 using a lateral approach. In afurther embodiment, the keel 124 may be angled, tapered, or configuredin some other shape to facilitate the functional demands of the keel. Instill another embodiment, the keel 124 may be configured as a wingedkeel, including a transverse portion extending across the main bodyportion of keel 124.

The keel 124 also includes openings 126 extending therethrough tofacilitate bone through-growth to enhance fixation to the adjacentvertebra. However, it should be understood that any number of openings126 may be defined through keel 124, including a single opening or threeor more openings. It should also be understood that the openings 104need not necessarily extend entirely through the keel 124, but mayalternatively extend partially therethrough. It should further beunderstood that the keel 124 need not necessarily define any openings126 extending either partially or entirely therethrough. Additionally,although the openings 126 are illustrated as having a circularconfiguration, it should be understood that other sizes andconfigurations of openings 126 are also contemplated. As discussedabove, the surfaces of the slidable component 112 that are in directcontact with vertebral bone are preferably coated with a bone-growthpromoting substance. Specifically, the bearing surface 120 and thesurfaces of the keel 124 can be coated with hydroxyapatite to promotebony engagement with the adjacent vertebrae. As also discussed above,the bearing surface 120 and the surfaces of keel 124 can be roughenedprior to application of the hydroxyapatite coating.

In one embodiment, the slidable component 114 includes a support plate128 having a slidable surface 130 and an opposite bearing surface 132.Support plate 128 is preferably sized and shaped to substantiallycorrespond to the size and shape of the vertebral endplate of anadjacent vertebra. The support plate 128 can include one or more notches134 or other types of indicia for receiving and engaging with acorresponding portion of a surgical instrument, such as discussed abovewith reference to slidable element 112.

A flange member or keel 136, configured similar to the keel 124 ofslidable component 112, extends from the bearing surface 132. In oneembodiment, the keel 136 extends perpendicularly from the bearingsurface 132 and is offset along the bearing surface 132 to accommodatespondylosed displacements of the vertebrae. Also, the offset position ofthe keel 136 helps in the circumvention of veins, arteries, bonyportions, or other obstacles that may be in place during the insertionof the joint 110. It should be further understood that other positions,shapes, orientations, and quantities of the keel 136 are alsocontemplated. It should also be understood that the keel 136 may also bedifferently positioned, shaped or oriented, or more keels 136 can beused, for similar or additional reasons.

In one embodiment, the keel 136 transversely extends along a substantialportion of the support plate 128. Such an embodiment would accommodateinsertion of the prosthetic joint 110 using a lateral approach asopposed to another approach such as an anterior approach. In a furtherembodiment, the keel 136 may be angled, tapered, or configured in someother shape to facilitate the functional demands of the keel. In stillanother embodiment, the keel 136 may be configured as a winged keel,including a transverse portion extending across the main body portion ofkeel 136.

The keel 136 also includes three openings 138 extending therethrough tofacilitate bone through-growth to enhance fixation to the adjacentvertebra. However, it should be, understood that any number of openings138 may be defined through keel 136, including a single opening or threeor more openings. It should also be understood that the openings 138need not necessarily extend entirely through the keel 136, but mayalternatively extend partially therethrough. It should further beunderstood that the keel 136 need not necessarily define any openings138 extending either partially or entirely therethrough. Additionally,although the openings 138 are illustrated as having a circularconfiguration, it should be understood that other sizes andconfigurations of openings 138 are also contemplated. As discussedabove, the surfaces of the slidable component 114 that are in directcontact with vertebral bone are preferably coated with a bone-growthpromoting substance. Specifically, the bearing surface 132 and thesurfaces of the keel 136 can be coated with hydroxyapatite to promotebony engagement with the adjacent vertebrae. As also discussed above,the bearing surface 132 and the surfaces of keel 136 can be roughenedprior to application of the hydroxyapatite coating.

In some embodiments, one or both of the keels 124, 136 may include asharp forward edge, illustrated by edges 124 a, 136 a. By having such anedge, insertion of the keels 124, 136 into the associated vertebral bodyis facilitated. Also, the edges 124 a, 136 a can be of sufficientsharpness that the vertebral body does not require a slot for receivingthe keels 124, 136, respectively, discussed in greater detail below.

Referring to FIG. 10, to accommodate insertion of the prosthetic joint110 within a spondylosed intervertebral space, the lower and uppervertebrae V_(L), V_(U) can be prepared to accept the prosthetic joint110 therebetween. Specifically, elongate openings or slots 142, 144, maybe formed along the vertebral endplates of the lower and upper vertebraeV_(L), V_(U), respectively, at a predetermined width and to apredetermined depth. The slots 142, 144 can be laterally offset fromeach other to accommodate the displaced vertebrae V_(L) and/or V_(U). Inone embodiment of the disclosure, the elongate slots 142, 144 arerectangular-shaped and extend laterally through the vertebrae V_(L),V_(U). In a specific embodiment, the slots 142, 144 are formed bychiseling or curetting. However, other methods of forming slots 142, 144are also contemplated as would occur to one of ordinary skill in theart, such as, for example, by drilling or reaming. Furthermore, for someembodiments of the prosthetic joint, the keels 124 and/or 136 can formtheir own corresponding slots.

Referring to FIG. 11, in one embodiment, the upper and lower vertebraeV_(U), V_(L) may be fully corrected, and thus, an alternativearticulating joint 150 may be used in correcting spondylolisthesis. Thearticulating joint 150 may be substantially similar to the articulatingjoint 110 with the exception of the orientation of the keel. Forexample, to accommodate insertion into fully corrected upper and lowervertebrae V_(U), V_(L), the articulating joint 150 may include a keel152 that is substantially centered on an upper articulating component154 of the articulating joint and a keel 156 that is substantiallycentered on a lower articulating component 158. In one embodiment, theupper and lower articulating components 154, 158 are substantially flushwith one another when disposed between fully corrected upper and lowervertebrae V_(U), V_(L).

To accommodate insertion of the offset prosthetic joint 150, the fullycorrected upper and lower vertebrae V_(U), V_(L) can be prepared toaccept the prosthetic joint 150 therebetween. Specifically, elongateopenings or slots 160, 162 are formed along the vertebral endplates ofthe upper and lower vertebrae V_(U), V_(L), at a predetermined width andto a predetermined depth. The slots 160, 162 can be substantiallyaligned with each other to accommodate the fully corrected upper andlower vertebrae V_(U), V_(L). In one embodiment, the elongate slots 160,162 are rectangular-shaped and extend laterally through the vertebraeV_(U), V_(L), respectively. In a specific embodiment, the slots 160, 162are formed by chiseling or curetting. However, other methods of formingslots 160, 162 are also contemplated as would occur to one of ordinaryskill in the art, such as, for example, by drilling or reaming.Furthermore, for some embodiments of the prosthetic joint, the keels 152and/or 156 can form their own corresponding slots 160, 162,respectively.

Referring to FIGS. 12 and 13, fusion plates and cages can also beoutfitted with one or more keels and laterally inserted, in a mannerconsistent with the motion-preserving embodiments discussed above andsuperior to conventional fusion arrangements. Referring specifically toFIG. 12, a lateral prosthesis 170 includes a cage 172, an upper keel174, and a lower keel 176. The cage 172 connects to the upper and lowerkeels 174, 176 through support plates 178, 180, respectively. The cage172 can include many features of the LT-CAGE™ lumbar tapered fusiondevice provided by Medtronic Sofamor Danek of Memphis, Tenn., and can beused to contain biological material and/or other bone growth promotingmaterials. Also, the lateral keels 174, 176 can help to maintain thecorrected vertebrae displacement while fusion is occurring.

Referring to FIG. 13, a prosthesis 190 includes a plate 192, an upperkeel 194, a lower keel 196, an upper support plate 198, and a lowersupport plate 200. The plate 192 can be used to maintain a desireddistance between the two support plates 198, 200 and promote fusion.Since the plate 192 can be relatively thin, the remainder of the discspace can be filled with biological material, bone material, and orother bone growth promoting materials.

II. Anterior Correction

In some instances, correction of spondylolisthesis may be desirable fromthe anterior approach. Referring to FIGS. 14-16, shown therein is anintervertebral articulating prosthetic joint 210 according to analternative embodiment of the present disclosure. The prosthetic joint210 extends generally along a longitudinal axis L and includes a firstarticular component 212 and a second articular component 214. Thearticular components 212, 214 cooperate to form the articulating joint210 which is sized and configured for disposition within anintervertebral space between a pair of vertebral bodies, such as theintervertebral space S between the adjacent vertebral bodies V_(U),V_(L).

The prosthetic joint 210 provides relative pivotal and rotationalmovement between the adjacent vertebral bodies V_(U), V_(L) to maintainor restore motion substantially similar to the normal bio-mechanicalmotion provided by a natural intervertebral disc. More specifically, thearticular components 212, 214 are permitted to pivot relative to oneanother about a number of axes, including lateral or side-to-sidepivotal movement about longitudinal axis L and anterior-posteriorpivotal movement about a transverse axis T. It should be understood thatin one embodiment, the articular components 212, 214 are permitted topivot relative to one another about any axes that lies in a plane thatintersects longitudinal axis L and transverse axis. T. Additionally, thearticular components 212, 214 are permitted to rotate relative to oneanother about a rotational axis R. Although the prosthetic joint 210 hasbeen illustrated and described as providing a specific combination ofarticulating motion, it should be understood that other combinations ofarticulating movement are also possible, such as, for example, relativetranslational or linear motion, and are contemplated as falling withinthe scope of the present disclosure.

Although the articular components 212, 214 of prosthetic joint 210 maybe formed from a wide variety of materials, in one embodiment, thearticular components 212, 214 are formed of a cobalt-chrome-molybdenummetallic alloy (ASTM F-799 or F-75). However, in alternativeembodiments, the articular components 212, 214 may be formed of othermaterials such as titanium or stainless steel, a polymeric material suchas polyethylene, or any other biocompatible material that would beapparent to one of ordinary skill in the art. The surfaces of thearticular components 212, 214 that are positioned in direct contact withvertebral bone may be coated with a bone-growth promoting substance,such as, for example, a hydroxyapatite coating formed of calciumphosphate. Additionally, the surface of the articular components 212,214 that are positioned in direct contact with vertebral bone may beroughened prior to being coated with the bone-growth promoting substanceto, further enhance bone on-growth. Such surface roughening may beaccomplished by way of, for example, acid etching, knurling, applicationof a bead coating, or other methods of roughening that would occur toone of ordinary skill in the art.

Articular component 212 includes a support plate 216 having an articularsurface 218 and an opposite bearing surface 220. Support plate 216 maybe sized and shaped to substantially correspond to the size and shape ofthe vertebral endplate of an adjacent vertebra. The support plate 216can include one or more notches 222 or other types of indicia forreceiving and engaging with a corresponding portion of a surgicalinstrument (not shown) to aid in the manipulation and insertion of thearticulating joint 210 within an intervertebral space between adjacentvertebrae. The surgical instrument (not shown) is preferably configuredto hold the articular components 212, 214 at a predetermined orientationand spatial relationship relative to one another during manipulation andinsertion of the articulating joint 210, and to release the articularcomponents 212, 214 once properly positioned between the adjacentvertebrae.

In one embodiment, the articular surface 218 includes a projection 224having a convex shape, which may be configured as a spherical-shapedball (half of which is shown). It should be understood that otherconfigurations of the projection 224 are also contemplated, such as, forexample, cylindrical, elliptical or other arcuate configurations orpossibly non-arcuate configurations. It should also be understood thatthe remaining portion of articular surface 218 may take on planar ornon-planar configurations, such as, for example, an angular or conicalconfiguration extending about the projection 224.

In one embodiment, the convex articular surface of the projection 224 isinterrupted by a surface depression or cavity 226 extending along theprojection 224. In one embodiment, the surface depression 226 isconfigured as a groove. However, it should be understood that othertypes of surface depressions are also contemplated, including nodepression at all. One purpose of the groove 226 is to facilitate theremoval of matter disposed between abutting portions of the articularcomponents 212, 214. More specifically, the groove 226 may aid inclearing out matter such as, for example, particulate material, that isdisposed between the abutting articular surfaces of components 212, 214.

A flange member or keel 230 extends from the bearing surface 220 and isconfigured for disposition within a preformed opening in the adjacentvertebral endplate. In one embodiment, the keel 230 extendsperpendicularly from the bearing surface 220 and is approximatelycentrally located along the bearing surface 220. However, it should beunderstood that other positions and orientations of the keel 230 arealso contemplated.

In one embodiment, the keel 230 extends along substantially the entirelength of the support plate 216. Such an embodiment would accommodateinsertion of the articulating joint 210 using an anterior approach. In afurther embodiment, the keel 230 may be angled, tapered, or configuredin some other shape to facilitate the functional demands of the keel. Instill another embodiment, the keel 230 may be configured as a wingedkeel, including a transverse portion (not shown) extending across themain body portion of keel 230.

The keel 230 also includes a pair of openings 232 extending therethroughto facilitate bone through-growth to enhance fixation to the adjacentvertebra. However, it should be understood that any number of openings232 may be defined through keel 230, including a single opening or threeor more openings. It should also be understood that the openings 232need not necessarily extend entirely through the keel 230, but mayalternatively extend partially therethrough. It should further beunderstood that the keel 230 need not necessarily define any openings232 extending either partially or entirely therethrough. Additionally,although the openings 232 are illustrated as having a circularconfiguration, it should be understood that other sizes andconfigurations of the openings 232 are also contemplated. As discussedabove, the surfaces of the articular component 212 that are in directcontact with vertebral bone are preferably coated with a bone-growthpromoting substance. Specifically, the bearing surface 220 and thesurfaces of the keel 230 can be coated with hydroxyapatite to promotebony engagement with the adjacent vertebrae. As also discussed above,the bearing surface 220 and the surfaces of keel 230 can be roughenedprior to application of the hydroxyapatite coating.

In one embodiment, the articular component 214 includes a support plate240 having an articular surface 242 and an opposite bearing surface 244.Support plate 240 may be sized and shaped to substantially correspond tothe size and shape of the vertebral endplate of an adjacent vertebra.The support plate 240 can include one or more notches 246 or other typesof indicia for receiving and engaging with a corresponding portion of asurgical instrument, such as discussed above with reference to articularcomponent 212.

In one embodiment, the articular surface 242 includes a recess 250,which has a convex shape, such as that of a spherical-shaped socket.However, it should be understood that other configurations of the recess250 are also contemplated, such as, for example, cylindrical, ellipticalor other arcuate configurations or possibly non-arcuate configurations.The remaining portion of the articular surface 242 can be angled orotherwise configured to facilitate the insertion and/or use of thearticulating joint 210.

Although the concave recess 250 is illustrated as having a generallysmooth, uninterrupted articular surface, it should be understood that asurface depression or cavity may be defined along a portion of therecess 250 to aid in clearing out matter, such as particulate debris,that is disposed between the abutting articular surfaces of articularcomponents 212, 214. In such case, the convex articular surface of theball 224 may alternatively define a generally smooth, uninterruptedarticular surface. In another embodiment, each of the convex projection224 and the concave recess 250 may define a surface depression tofacilitate removal of particulate matter disposed between the abuttingarticular surfaces.

A flange member or keel 260, configured similar to the keel 230 ofarticular component 212, extends from the bearing surface 244. In oneembodiment, the keel 260 extends perpendicularly from the bearingsurface 244 and is approximately centrally located along bearing surface244. However, it should be understood that other positions andorientations of the keel 260 are also contemplated. It should also beunderstood that the articular component 214 may include two or morekeels 260 extending from the bearing surface 244.

In one embodiment, the keel 260 extends along substantially the entirelength of the support plate 240. Such an embodiment would accommodateinsertion of the prosthetic joint 210 using an anterior approach. In afurther embodiment, the keel 260 may be angled, tapered, or configuredin some other shape to facilitate the functional demands of the keel. Instill another embodiment, the keel 260 may be configured as a wingedkeel, including a transverse portion (not shown) extending across themain body portion of keel 260.

The keel 260 also includes a pair of openings 262 extending therethroughto facilitate bone through-growth to enhance fixation to the adjacentvertebra. However, it should be understood that any number of openings262 may be defined through keel 260, including a single opening or threeor more openings. It should also be understood that the openings 262need not necessarily extend entirely through the keel 260, but mayalternatively extend partially therethrough. It should further beunderstood that the keel 260 need not necessarily define any openings262 extending either partially or entirely therethrough. Additionally,although the openings 262 are illustrated as having a circularconfiguration, it should be understood that other sizes andconfigurations of openings 262 are also contemplated. As discussedabove, the surfaces of the articular component 214 that are in directcontact with vertebral bone are preferably coated with a bone-growthpromoting substance. Specifically, the bearing surface 244 and thesurfaces of the keel 260 can be coated with hydroxyapatite to promotebony engagement with the adjacent vertebrae. As also discussed above,the bearing surface 244 and the surfaces of keel 260 can be roughenedprior to application of the hydroxyapatite coating.

In some embodiments, one or both of the keels 230, 260 may include asharp forward edge, illustrated by edge 260 a of FIG. 14. By having suchan edge, insertion of the keel into the associated vertebral body isfacilitated. Also, the edge 260 a can be of sufficient sharpness thatthe vertebral body does not require a slot for receiving the keel 260,discussed in greater detail below.

To work with dislocated vertebrae, such as vertebrae V1-V5 of FIG. 1associated with spondylolisthesis, it is recognized that the task offully correcting and aligning a spondylosed segment may not beachievable or desirable by the surgeon. Therefore, the basicarticulation described in co-pending and presently incorporated U.S.Ser. No. 10/042,589 now has an associated displacement to correspond tothe vertebrae displacement. That is, for the amount of displacementbetween two adjacent spondylosed vertebrae, the articulation of theprosthetic joint 210 is made to correspond thereto. In some embodiments,such displacement can be effected by positioning one or more of theprojection 224 in an offset position on the articular surface 218 of thearticular component 212; and positioning one or more of the recess 250in an offset position on the articular surface 242 of the articularcomponent 214. This allows an uncorrected or partially correcteddisplacement to be mobilized.

More particularly, and referring to FIGS. 14 and 17, the projection 224is offset relative to the articular surface 218. For example, when thelower vertebra (V_(L) of FIG. 17) is offset in the posterior direction(illustrated by arrow P in FIG. 17), the articular component 212 may beconfigured such that the projection 224 is offset in the anteriordirection relative to the articular surface 218. Continuing thisexample, the upper vertebra V_(U) is therefore offset from the lowervertebra V_(L) in the anterior direction (illustrated by arrow A in FIG.17), and thus, the articular component 214 may be configured such thatthe recess 250 is offset in the posterior direction relative to thearticular surface 242. In this manner, the articular components 212, 214can be configured to engage one another via the projection 224 and therecess 250, yet be offset from one another to accommodate thespondylosed relationship of the upper and lower vertebrae V_(U), V_(L)of FIG. 17.

Referring now to FIG. 16, in another embodiment, the articulating joint210 may be modified such that the support plate 216 includes an extendedsection 270 to accommodate a more pronounced displacement relative toFIG. 17 (illustrated by arrow 272) and/or provide additional stabilityagainst subluxation. The projection 224 may be positioned on theextended section 270 to provide for the more pronounced displacementbetween articular components 212, 214.

Referring to FIGS. 2 and 17, to accommodate insertion of the prostheticjoint 210 within the intervertebral space S, the upper and lowervertebrae V_(U), V_(L), can be prepared to accept the prosthetic joint210 therebetween. Specifically, elongate openings or slots 280, 282 areformed along the vertebral endplates of the upper and lower vertebraeV_(U), V_(L), respectively, at a predetermined width and to apredetermined depth. In one embodiment, the elongate slots 280, 282 arerectangular-shaped and extend from an anterior side 284 of the vertebraeV_(U), V_(L), toward a posterior side. In a specific embodiment, theslots 280, 282 are formed by chiseling or curetting. However, othermethods of forming the slots 280, 282 are also contemplated as wouldoccur to one of ordinary skill in the art, such as, for example, bydrilling or reaming. Furthermore, for some embodiments of the prostheticjoint 210, the keels 230 and/or 260 can form their own correspondingslots 280, 282, respectively. The preparation and example sizes of theslots 280, 282 are described in further detail in co-pending andpresently incorporated U.S. Ser. No. 10/042,589.

Referring now to FIGS. 18-20, in other embodiments, one or both of thearticular components 212, 214 may include different numbers of keelsand/or modified keels. Referring specifically to FIG. 18, two keels,designated 290 and 292, extend from the bearing surface 244 and areconfigured for disposition within preformed openings in the adjacentvertebral endplate. In one embodiment, both keels 290, 292 extendperpendicularly from the bearing surface 244 and are parallel andequally spaced along a central portion of the bearing surface 244.

Referring specifically to FIG. 19, two keels, designated 294 and 296,extend from the bearing surface 224 and are configured for dispositionwithin preformed openings in the adjacent vertebral endplate. In oneembodiment, both keels 294, 296 extend perpendicularly from the bearingsurface 224 and are parallel and equally spaced along a central portionof the bearing surface 224. It should be understood that other positionsand orientations of the keels 290, 292, 294, and 296 are alsocontemplated.

Referring specifically to FIG. 20, a keel 298 extends from the bearingsurface 244 similar to the keel 260 of FIG. 14, except that the keel 298includes a laterally-extending or “winged” portion 300 opposing thebearing surface 244. The winged portion 300 can provide severalfunctions, including maintaining the bearing surface 244 tightly againstthe body Vu, and substantially preventing any longitudinal movement ofthe articular component 214. Similarly, a keel 302 extends from thebearing surface 224 and includes a winged portion 304 opposing thebearing surface 224. The winged portion 304 can provide severalfunctions, including maintaining the bearing surface 224 tightly againstthe body V_(L), and substantially preventing any longitudinal movementof the articular component 212.

Referring to FIGS. 21-23; to accommodate insertion of theabove-described alternative prosthetic joints 210 within theintervertebral space S, the upper and lower vertebrae V_(U), V_(L), canbe prepared to accept each of the articulating joints 210 therebetween.Referring specifically to FIG. 21, for the configuration of theprosthetic joint 210 of FIG. 18, multiple slots 310 and 312 are formedalong the vertebral endplate of the upper vertebrae V_(U), and a singleslot 314 is formed along the vertebral endplate of the lower vertebraeV_(L). Referring specifically to FIG. 22, for the configuration of theprosthetic joint 210 of FIG. 19, multiple slots 316, 318 and 320, 322are formed along the vertebral endplates of the upper vertebrae V_(U),and lower vertebrae V_(L), respectively. Referring specifically to FIG.23, for the configuration of the prosthetic joint 210 of FIG. 20, wingedslots 324, 326 are formed along the vertebral endplates of the uppervertebrae V_(U) and the lower vertebrae V_(L), respectively. Thepreparation of the slots 310, 312, 314, 316, 318, 320, 322, 324, 326 canbe accomplished in a similar manner to those discussed above withrespect to FIG. 17. For the winged slots 324, 326, a standard chisel canbe used, or alternatively, a unique wing-shaped chisel can be used.

Referring to FIG. 24, in addition to the prosthetic joint 210, a wovenorthopedic implant 330 can be used to act as an artificial ligamentbetween the two vertebrae V_(U), V_(L). One embodiment of the wovenimplant 330 is disclosed in U.S. Ser. No. 10/082,579, which isincorporated by reference. The implant 330 functions as a naturalligament would function, and helps to stabilize and further secure thetwo vertebrae V_(U), V_(L) together, and helps to discourage furtherdisplacement (or prevent the displacement from returning to the way itwas pre-surgery).

Referring to FIGS. 25 and 26, it is contemplated that a pars fracture,such as is illustrated by a fracture in a bony element 332 that connectsa posterior element, such as an articular process 334 to the vertebraV_(L), may also be treated during correction of spondylolisthesis fromthe anterior approach. It is understood that the fractured bony element332 is exaggerated in the FIG. 25 for the sake of improved clarity. Thepars fracture can be repaired by driving a lag screw 336 having athreaded portion 336 a and a non-threaded portion 336 b into an opening338 in the vertebral body V_(L), through the bony element 332, and intothe articular process 334. In some embodiments, all or part of theopening 338 can be pre-drilled with a drill or chisel (not shown). Thelag screw 336 is inserted and accessed through the anterior direction,and multiple screws can be used to repair multiple processes. Bycapturing the fractured posterior element and tightening the lag screw336, the vertebrae V_(L), is repaired.

III. Transforaminal Prosthetic Joint

In some instances, it is often difficult to approach and clear adefective intervertebral disc space due to potential damage to importantanatomical structures such as nerve roots, dura, ligamentum flavum andinterspinous ligament. For example, preservation of the ligamentousstructures is of great importance to restore biomechanical stability ofthe segment and its adjacent counterparts. In these situations, atransforaminal approach may allow clearance of the entire intervertebraldisc space by opening the neuroforamen on one side. After appropriateclearance, it is possible to achieve further enlargement of the clearedintervertebral compartment by posterior trans-pedicle distraction. Whilethis approach has been used for fusion techniques, such asTransforaminal Lumbar Interbody Fusion, or TLIF, it has not heretoforebeen used with motion preserving implants.

Referring to FIG. 27, in a transforaminal approach, the disc V isapproached as shown by the arrow 400. The approach is between aposterior approach and a lateral approach, and in some cases, only oneside of the disc needs to be exposed (right or left) in order to performthe procedure.

Referring to FIGS. 28-30, shown therein is an intervertebralarticulating prosthetic joint 410 according to another form of thepresent disclosure. The articulating joint 410 extends generally along alongitudinal axis L and includes a first articular component 412 and asecond articular component 414. The articular components 412, 414cooperate to form the articulating joint 410 which is sized andconfigured for disposition within an intervertebral space betweenadjacent vertebral bodies.

The prosthetic joint 410 provides relative pivotal and rotationalmovement between the adjacent vertebral bodies to maintain or restoremotion substantially similar to the normal bio-mechanical motionprovided by a natural intervertebral disc. More specifically, thearticular components 412, 414 are permitted to pivot relative to oneanother about a number of axes, including lateral or side-to-sidepivotal movement about longitudinal axis L and anterior-posteriorpivotal movement about a transverse axis T. It should be understood thatin one embodiment, the articular components 412, 414 are permitted topivot relative to one another about any axes that lies in a plane thatintersects longitudinal axis L and transverse axis T. Additionally, thearticular components 412, 414 are preferably permitted to rotaterelative to one another about a rotational axis R. Although thearticulating joint 410 has been illustrated and described as providing aspecific combination of articulating motion, it should be understoodthat other combinations of articulating movement are also possible andare contemplated as falling within the scope of the present disclosure.It should also be understood that other types of articulating movementare also contemplated, such as, for example, relative translational orlinear motion.

Although the articular components 412, 414 of prosthetic joint 410 maybe formed from a wide variety of materials, in one embodiment, thearticular components 412, 414 are formed of a cobalt-chrome-molybdenummetallic alloy (ASTM F-799 or F-75). However, in alternativeembodiments, the articular components 412,414 may be formed of othermaterials such as titanium or stainless steel, a polymeric material suchas polyethylene, or any other biocompatible material that would beapparent to one of ordinary skill in the art. The surfaces of thearticular components 412, 414 that are positioned in direct contact withvertebral hone are preferably coated with a bone-growth promotingsubstance, such as, for example, a hydroxyapatite coating formed ofcalcium phosphate. Additionally, the surface of the articular components412, 414 that are positioned in direct contact with vertebral bone arepreferably roughened prior to being coated with the bone-growthpromoting substance to further enhance bone on-growth. Such surfaceroughening may be accomplished by way of, for example, acid etching,knurling, application of a bead coating, or other methods of rougheningthat would occur to one of ordinary skill in the art.

Articular component 412 includes a support plate 416 having an articularsurface 418 and an opposite bearing surface 420. Support plate 416 maybe sized and shaped to substantially correspond to the size and shape ofthe vertebral endplate of an adjacent vertebra. In one embodiment, thesupport plate 416 is shaped to facilitate a transforaminal insertionapproach. As such, the support plate 416 includes curved side portions422 a, 422 b, which are defined as the generally elongated portions ofthe support plate 416 extending between articular surface 418 and thebearing surface 420. Although not shown, the support plate 416 caninclude one or more notches or other types of indicia for receiving andengaging with a corresponding portion of a surgical instrument (also notshown) to aid in the manipulation and insertion of the prosthetic joint410 within an intervertebral space between adjacent vertebrae. Thesurgical instrument (not shown) is preferably configured to hold thearticular components 412, 414 at a predetermined orientation and spatialrelationship relative to one another during manipulation and insertionof the prosthetic joint 410, and to release the articular components412, 414 once properly positioned between the adjacent vertebrae.

In one embodiment, the articular surface 418 includes a projection 424having a convex shape, which may be configured as a spherical-shapedball (half of which is shown). It should be understood that otherconfigurations of the projection 424 are also contemplated, such as, forexample, cylindrical, elliptical or other arcuate configurations orpossibly non-arcuate configurations. It should also be understood thatthe remaining portion of articular surface 418 may take on planar ornon-planar configurations, such as, for example, an angular or conicalconfiguration extending about the projection 424.

A flange member or keel 426 extends from the bearing surface 410 and isconfigured for disposition within a preformed opening in the adjacentvertebral endplate. In one embodiment, the keel 426 extendsperpendicularly from the bearing surface 420 and is approximatelycentrally located along the bearing surface 420. However, it should beunderstood that other positions and orientations of the keel 426 arealso contemplated.

In one embodiment, the keel 426 transversely extends along a substantialportion of the support plate 416. The keel 426 is curved, generally in adirection similar to the arrow 400 of FIG. 27. The degree of curvatureof the keel 426 may be substantially similar to and congruous with thedegree of curvature of the side portions 422 a, 422 b. Such anembodiment would accommodate insertion of the prosthetic joint 410 usinga transforaminal approach as opposed to the anterior or lateralapproaches discussed above. In a further embodiment, the keel 426 may beangled, tapered, or configured in some other shape to facilitate thefunctional demands of the keel. In still another embodiment, the keel426 may be configured as a winged keel, including a transverse portion(not shown) extending across the main body portion of keel 426.

The keel 426 also includes three openings 428 extending therethrough tofacilitate bone through-growth to enhance fixation to the adjacentvertebra. However, it should be understood that any number of openings428 may be defined through keel 426, including a single opening or threeor more openings. It should also be understood that the openings 428need not necessarily extend entirely through the keel 426, but mayalternatively extend partially therethrough. It should further beunderstood that the keel 426 need not necessarily define any openings428 extending either partially or entirely therethrough. Additionally,although the openings 428 are illustrated as having a circularconfiguration, it should be understood that other sizes andconfigurations of openings 428 are also contemplated. As discussedabove, the surfaces of the articular component 412 that are in directcontact with vertebral bone are preferably coated with a bone-growthpromoting substance. Specifically, the bearing surface 420 and thesurfaces of the keel 426 can be coated with hydroxyapatite to promotebony engagement with the adjacent vertebrae. As also discussed above,the bearing surface 420 and the surfaces of keel 426 can be roughenedprior to application of the hydroxyapatite coating.

In one embodiment, the articular component 414 includes a support plate430 having an articular surface 432 and an opposite bearing surface 434.Support plate 430 may be sized and shaped to substantially correspond tothe size and shape of the vertebral endplate of an adjacent vertebra. Inone embodiment, the support plate 430 is shaped to facilitate atransforaminal insertion approach. As such, the support plate 416includes curved side portions 436 a, 436 b, which are defined as thegenerally elongated portions of the support plate 430 extending betweenarticular surface 432 and the bearing surface 434. Although not shown,the support plate 430 can include one or more notches or other types ofindicia for receiving and engaging with a corresponding portion of asurgical instrument, such as discussed above with reference to articularelement 412.

In one embodiment, the articular surface 432 includes a recess 440having a concave shape, which may be configured as a spherical-shapedsocket. However, it should be understood that other configurations ofthe recess 440 are also contemplated, such as, for example, cylindrical,elliptical or other arcuate configurations or possibly non-arcuateconfigurations. The remaining portion of the articular surface 432 canbe angled or otherwise configured to facilitate the insertion and/or useof the prosthesis.

Although the concave recess 440 is illustrated as having a generallysmooth, uninterrupted articular surface, it should be understood that asurface depression or cavity may be defined along a portion of therecess 440 to provide a means for clearing out matter, such asparticulate debris, that is disposed between the abutting articularsurfaces of components 412, 414. In such case, the convex articularsurface of the ball 424 may alternatively define a generally smooth,uninterrupted articular surface. In another embodiment, each of theconvex projection 424 and the concave recess 440 may define a surfacedepression to facilitate removal of particulate matter disposed betweenthe abutting articular surfaces.

A flange member or keel 450, configured similar to the keel 426 ofarticular component 412, extends from the bearing surface 434. In oneembodiment, the keel 450 can be centrally located, and is positioneddirectly or parallel in-line with the keel 450. The keel 450 is curved,in a direction similar to the keel 426 and the arrow 400 of FIG. 27. Thedegree of curvature of the keel 450 may be substantially similar to andcongruous with the degree of curvature of the side portions 436 a, 436b. Such an embodiment would accommodate insertion of the prostheticjoint 410 using a transforaminal approach as opposed to the anterior orlateral approaches discussed above. In some embodiments, the position ofthe keel 450 can be offset to help circumvent veins, arteries, bonyportions, or other obstacles that may be in place during the insertionof the joint 410.

It should also be understood that the keel 450 may also be differentlypositioned, shaped or oriented, or more keels 450 can be used, forsimilar or additional reasons. Also, the keel 450 may be angled,tapered, or configured in some other shape to facilitate the functionaldemands of the keel. In still another embodiment, the keel 450 may beconfigured as, a winged keel, including a transverse portion (not shown)extending across the main body portion of keel 450.

In one embodiment, the keel 450 also includes three openings 452extending therethrough to facilitate bone through-growth to enhancefixation to the adjacent vertebra. However, it should be understood thatany number of openings 452 may be defined through keel 450, including asingle opening or three or more openings. It should also be understoodthat the openings 452 need not necessarily extend entirely through thekeel 450, but may alternatively extend partially therethrough. It shouldfurther be understood that the keel 450 need not necessarily define anyopenings 452 extending either partially or entirely therethrough.Additionally, although the openings 452 are illustrated as having acircular configuration, it should be understood that other sizes andconfigurations of openings 452 are also contemplated. As discussedabove, the surfaces of the articular component 414 that are in directcontact with vertebral bone are preferably coated with a bone-growthpromoting substance. Specifically, the bearing surface 434 and thesurfaces of the keel 450 can be coated with hydroxyapatite to promotebony engagement with the adjacent vertebrae. As also discussed above,the bearing surface 434 and the surfaces of keel 450 can be roughenedprior to application of the hydroxyapatite coating.

In some embodiments, one or both of the keels 426, 450 may include asharp forward edge, illustrated by edges 460, 462, respectively, of FIG.28 c. By having such an edge, insertion of the keel into the associatedvertebral body is facilitated. Also, the edges 460, 462 can be ofsufficient sharpness that the vertebral bodies do not require a slot forreceiving the keels 426, 450, discussed in greater detail below.

Referring to FIGS. 31 a and 31 b, to accommodate insertion of theprosthetic joint 410 within the intervertebral space, the upper andlower vertebrae V_(U), V_(L), can be prepared to accept the prostheticjoint 410 therebetween. Referring specifically to FIG. 31 a, for theconfiguration of the prosthetic joint 410 of FIGS. 28-30, multiple slots470, 472 are formed along the vertebral endplates of the upper vertebraeV_(U) and the lower vertebrae V_(L). The slots 470, 472 can be createdby the keels 426, 450 themselves, or can be prepared beforehand.

Referring also to FIG. 32, it may be desirable to prepare one or more ofthe slots 470, 472 before the prosthetic joint 410 is inserted betweenthe upper and lower vertebrae V_(U), V_(L). The slots 470, 472 can becurved, as illustrated by the slot 472, in accordance with the curvedkeels 426, 450, to facilitate the movement of the prosthetic joint 410during insertion.

Referring to FIGS. 33-35, as an alternative to chiseling, which providesonly for the cutting of straight slots, a milling guide 500 may be usedin conjunction with a milling tool 502 to cut the curved slots 470, 472(represented by 472 in FIG. 32) in the upper and lower vertebral boneV_(U), V_(L). The milling guide 500 and milling tool 502 may be formedof any material including biocompatible materials such as titanium. Themilling guide 500 includes an elongated curved member 503, which definesa curved opening 504 to correspond to the shape of the desired curve forthe slots 470, 472. Of course, the degree of curvature of the millingguide 500, and therefore the curved opening 504, may vary depending onthe desired curve of the slots 470, 472. In one embodiment, the millingguide 500 is formed of a pliable material that retains a rigid shapeupon reforming such that the degree of curvature of the curved opening504 may be altered without having to swap out milling guides. Themilling guide 500, and therefore the curved opening 504, is also ofsufficient length so that if the slots 470, 472 need to be continuedthrough any posterior elements of the vertebrae, such extension of theslots can be accomplished at the same time.

Referring specifically to FIGS. 34 a and 34 b, in one embodiment, themilling tool 502 includes a milling bit 510 that is positioned to berotated and translated in the curved opening 504. In one embodiment, themilling bit 510 is a double fluted routing bit, that may extendsimultaneously into the upper and lower vertebrae V_(U), V_(L).

The milling bit 510 is also adapted to receive a translational forcesuch that the milling bit can be moved back and forth in the curvedopening 504. Referring to FIG. 34 b, in one embodiment, a milling bithandle 530 is connected in any conventional manner to a housing 522 (aportion of which is shown). The handle 530 extends from the housing 522and through a slot 532 formed in a proximal end 534 of the milling guide500 relative to a surgeon (not depicted). As such, the handle 530 can betranslated by a surgeon, thereby translating the milling bit 510 throughthe curved opening 504. In this manner, the handle 530 is adapted toimpart translational movement to the milling bit 510. To accommodatemovement of the milling bit 510 within the curved opening 504, a pair ofbearing assemblies 512, 514 may be positioned adjacent to the housing522 to guide the milling bit 510 along the curved opening.

The housing 522 houses a rotation assembly, which, in one embodiment, isa gear assembly 524. The gear assembly 524 includes a drive gear 526connected to and extending annularly around a rotatable shaft 528. Theshaft 528 is rotatable via an external source represented by powersupply 516 (FIG. 35). In one embodiment, the shaft 528 is housed withinthe handle 530.

The gear assembly 524 further includes a bit gear 530, which isconnected to and extends annularly around the milling bit 510. The bitgear 530 is positioned on the milling bit 510 such that the bit gear isorthogonal relative to and in contact with the drive gear 526. Thus,rotation of the shaft 528 imparts rotation to the milling bit 510 viathe gear assembly 524. A pair of annular shoulders 534, 536 are alsoconnected to the milling bit 510 such that the milling bit can easilymove back and forth through the curved opening 504 without slippage inthe upper or lower directions as viewed in FIG. 34 b. It is understoodthat the gear assembly 524 is merely exemplary of an assembly that maybe used to impart rotational motion to the milling bit 510. Other typesof rotation-imparting assemblies are contemplated as falling within thepresent disclosure such as pneumatic-type systems.

Referring to FIG. 34 c, in one such embodiment, a pneumatic system 538may be employed to impart rotation to the milling bit 510. In oneembodiment, a Medtronic Midas Rex® Legend™ motor is used to supply power(represented by P) to the pneumatic system. A conventional valve 539 isused to control the air flow and pressure supplied to rotate the millingbit 510. In still other embodiments, manual or combination powersupplies are contemplated as being the preferred power supply 516 (FIG.34 b) and P (FIG. 34 c).

Referring again to FIGS. 34 a and 34 b, a guide handle 540 is furtherprovided such that the milling guide 500 is independently movablerelative to the milling bit 510. Thus in one embodiment, the millingguide 500 can be held via the guide handle 540 with one hand while themilling bit 510 may be moved within the curved opening 504 via thehandle 530 with the other hand. In some embodiments, the handle 530 mayextend through the guide handle 540 as shown in FIG. 34 b. As a result,and referring to FIG. 35, the milling bit 510 is adapted to rotate in adirection indicated by arrow R1, and is adapted to be translated throughthe curved opening 504 in the directions indicated by arrow R2.

In operation, the milling guide 500 and the milling tool 502 can be usedto cut a slot, such as the slot 472, to prepare the vertebral body V_(L)to receive the lower portion of the prosthetic joint 410. The surgeonfirst selects the desired amount of curvature to impart to the slot 472and selects or configures the corresponding milling guide 500. Thesurgeon then approaches the vertebral body V_(L) from the transforaminalapproach to position the milling guide 500 into the disc space betweenthe upper and lower vertebrae V_(U), V_(L) and to abut the milling bit510 against the upper and lower vertebrae V_(U), V_(L). Upon properpositioning, the surgeon may then actuate the milling tool, 502 via thepower supply 516 to begin cutting into the upper and lower vertebraeV_(U), V_(L) with the milling bit 510.

The milling guide 500 may be held by the surgeon or via an externalinstrument such that the milling guide is stationary duringtranslational movement of the milling bit 510 through the milling guide.The curvature of the milling guide 500 guides the milling bit 510transforaminally through the upper and lower vertebrae V_(U), V_(L) tocut a transforaminal slot, such as the slot 472 depicted in the lowervertebra V_(L) FIG. 32, to prepare the upper and lower vertebrae toreceive the transforaminal prosthetic joint 410.

In an alternative embodiment, the keels of the prosthetic joint 410 maytake alternative shapes and configurations to assist in the curved,transforaminal approach used in inserting the joint. Referring to FIGS.36-38, the keels, designated 550 and 560, extend from the bearingsurfaces 434 and 420, respectively. The keels 550, 560 are relativelyshort and thus extend along a short portion of the bearing surfaces 434,420, respectively, in comparison to the keels 450, 426 of FIGS. 28-30.The relative shortness of the keels 550, 560 may aid such keels infollowing the openings 470, 472, respectively. In addition, theshortness of the keels 550, 560 and the ease with which such keelsfollow the openings 470, 472, respectively, allows the keels to beconfigured as either straight or curved keels, which increases thedesign options of the prosthetic joint 410. The keels 550, 560 may alsobe tapered to assist in insertion of the keels into the upper and lowervertebrae V_(U), V_(L).

IV. Anterior-Oblique Prosthetic Joint

Another approach that can be used to avoid potential damage to importantanatomical structures such as nerve roots, dura, ligamentum flavum andinterspinous ligament is the anterior oblique approach. For example, thestraight anterior approach to the disc space between vertebra L4 and L5,as well as the superior disc levels, can present high surgical risksduring the insertion of a total disc replacement implant because of theattachment of the major vessels to the anterior aspect of the spine.

Referring to FIGS. 39-41, shown therein is an intervertebralarticulating prosthetic joint 600 according to another form of thepresent disclosure. The prosthetic joint 600 extends generally along alongitudinal axis L and includes a first articular component 602 and asecond articular component 604. The articular components 602, 604cooperate to form the prosthetic joint 600 which is sized and configuredfor disposition within an intervertebral space between adjacentvertebral bodies.

The prosthetic joint 600 provides relative pivotal and rotationalmovement between the adjacent vertebral bodies to maintain or restoremotion substantially similar to the normal bio-mechanical motionprovided by a natural intervertebral disc. More specifically, thearticular components 602, 604 are permitted to pivot relative to oneanother about a number of axes, including lateral or side-to-sidepivotal movement about longitudinal axis L and anterior-posteriorpivotal movement about a transverse axis T. It should be understood thatin a preferred embodiment, the articular components 602, 604 arepermitted to pivot relative to one another about any axes that lies in aplane that intersects longitudinal axis L and transverse axis T.Additionally, the articular components 602, 604 may be permitted torotate relative to one another about a rotational axis R. Although thearticulating joint 600 has been illustrated and described as providing aspecific combination of articulating motion, it should be understoodthat other combinations of articulating movement are also possible andare contemplated as falling within the scope of the present disclosure.It should also be understood that other types of articulating movementare also contemplated, such as, for example, relative translational orlinear motion.

Although the articular components 602, 604 of prosthetic joint 600 maybe formed from a wide variety of materials, in one embodiment, thearticular components 602, 604 are formed of a cobalt-chrome-molybdenummetallic alloy (ASTM F-799 or F-75). However, in alternative embodimentsof the invention, the articular components 602, 604 may be formed ofother materials such as titanium or stainless steel, a polymericmaterial such as polyethylene, or any other biocompatible material thatwould be apparent to one of ordinary skill in the art. The surfaces ofthe articular components 602, 604 that are positioned in direct contactwith vertebral bone are preferably coated with a bone-growth promotingsubstance, such as, for example, a hydroxyapatite coating formed ofcalcium phosphate. Additionally, the surface of the articular components602, 604 that are positioned in direct contact with vertebral bone arepreferably roughened prior to being coated with the bone-growthpromoting substance to further enhance bone on-growth. Such surfaceroughening may be accomplished by way of, for example, acid etching,knurling, application of a bead coating, or other methods of rougheningthat would occur to one of ordinary skill in the art.

Articular component 602 includes a support plate 610 having an articularsurface 612 and an opposite bearing surface 614. Support plate 610 maybe sized and shaped to substantially correspond to the size and shape ofthe vertebral endplate of an adjacent vertebra. In one embodiment, thesupport plate 610 is shaped in a triangular-like configuration tofacilitate an oblique insertion approach from either the left or rightside of the spine, and as such, includes side portions P1, P2 and P3.The side portions P1 , P2 and P3 may take a variety of configurationsincluding curved (illustrated by P2) or straight (illustrated by P1 andP3) configurations.

The support plate 610 can include one or more notches 616 or other typesof indicia for, receiving and engaging with a corresponding portion of asurgical instrument (also not shown) to aid in the manipulation andinsertion of the prosthetic joint 600 within an intervertebral spacebetween adjacent vertebrae. The surgical instrument (not shown) ispreferably configured to hold the articular components 602, 604 at apredetermined orientation aid spatial relationship relative to oneanother during manipulation and insertion of the prosthetic joint 600,and to release the articular components 602, 604 once properlypositioned between the adjacent vertebrae.

In one embodiment, the articular surface 612 includes a projection 620having a convex shape, which may be configured as a spherical-shapedball (half of which is shown). It should be understood that otherconfigurations of the projection 620 are also contemplated, such as, forexample, cylindrical, elliptical or other arcuate configurations orpossibly non-arcuate configurations. It should also be understood thatthe remaining portion of articular surface 612 may take on planar ornon-planar configurations, such as, for example, an angular or conicalconfiguration extending about the projection 620.

A flange member or keel 640 extends from the bearing surface 614 and isconfigured for disposition within a preformed opening in the adjacentvertebral endplate. In one embodiment, the keel 640 extendsperpendicularly from the bearing surface 614 and is approximatelycentrally located along the bearing surface 614. However, it should beunderstood that other positions and orientations of the keel 640 arealso contemplated. Furthermore, more keels 640 can be used, for similaror additional reasons.

In one embodiment, the keel 640 extends along a substantial portion ofthe support plate 610. The keel 640 is straight, but extends along adirection towards the notches 616 and is parallel with one of the sideportions P1 of the support plate 610. In the present example, the keel640 is positioned between the transverse axis T and lateral axis L. Suchan embodiment accommodates insertion of the prosthetic joint 600 usingan oblique approach as opposed to the anterior, lateral, ortransforaminal approaches discussed above. In a further embodiment, thekeel 640 may be angled, tapered, or configured in some other shape tofacilitate the functional demands of the keel. In still anotherembodiment, the keel 640 may be configured as a winged keel, including atransverse portion (not shown) extending across the main body portion ofkeel 640.

The keel 640 also includes a pair of openings 646 extending therethroughto facilitate bone through-growth to enhance fixation to the adjacentvertebra. Additionally, a gap 648 may also be formed in the keel 640 tofurther facilitate bone through-growth. The gap 648 also provides areference point such that an X-ray can be used to evaluate thepositioning and alignment of the support plate 602 during insertion ofthe prosthetic joint 600. It should be understood that any number ofopenings 646 or gaps 648 may be defined through keel 640, including asingle opening or gap or several openings and gaps. It should also beunderstood that the openings 646 and gap 648 need not necessarily extendentirely through the keel 640, but may alternatively extend partiallytherethrough. It should further be understood that the keel 640 need notnecessarily define any openings 646 or gaps 648 extending eitherpartially or entirely therethrough. Additionally, although the openings646 are illustrated as having a circular configuration, it should beunderstood that other sizes and configurations of openings 646 are alsocontemplated. As discussed above, the surfaces of the articularcomponent 602 that are in direct contact with vertebral bone may becoated with a bone-growth promoting substance. Specifically, the bearingsurface 614 and the surfaces of the keel 640 can be coated withhydroxyapatite to promote bony engagement with the adjacent vertebrae.As also discussed above, the bearing surface 614 and the surfaces ofkeel 640 can be roughened prior to application of the hydroxyapatitecoating.

In one embodiment, the articular component 604 includes a support plate650 having an articular surface 652 and an opposite bearing surface 654.Support plate 650 may be sized and shaped to substantially correspond tothe size and shape of the vertebral endplate of an adjacent vertebra. Inone embodiment, the support plate 610 is shaped in a triangular-likeconfiguration to facilitate an oblique insertion approach from eitherthe left or right side of the spine, and as such, includes side portionsP4, P5 and P6. The side portions P4, P5 and P6 may take a variety ofconfigurations including curved (illustrated by P5) or straight(illustrated by P4 and P6) configurations. The support plate 650 caninclude one or more notches 656 or other types of indicia for receivingand engaging with a corresponding portion of a surgical instrument, suchas discussed above with reference to articular component 602.

In one embodiment, the articular surface 652 includes a recess 660having a convex shape, which may be configured as a spherical-shapedsocket. However, it should be understood that other configurations ofthe recess 660 are also contemplated, such as, for example, cylindrical,elliptical or other arcuate configurations or possibly non-arcuateconfigurations. The remaining portion of the articular surface 652 canbe angled or otherwise configured to facilitate the insertion and/or useof the prosthesis.

Although the concave recess 660 is illustrated as having a generallysmooth, uninterrupted articular surface, it should be understood that asurface depression or cavity may be defined along a portion of therecess 660 to provide a means for clearing out matter, such asparticulate debris, that is disposed between the abutting articularsurfaces of components 602, 604. In such case, the convex articularsurface of the ball 620 may alternatively define a generally smooth,uninterrupted articular surface. In another embodiment of the invention,each of the convex projection 620 and the concave recess 660 may definea surface depression to facilitate removal of particulate matterdisposed between the abutting articular surfaces.

A flange member or keel 670, configured similar to the keel 640 ofarticular component 602, extends from the bearing surface 654. In oneembodiment, the keel 670 can be centrally located, and is positioneddirectly or parallel in-line with the keel 640. The keel 640 isstraight, but extends along a direction towards the notches 656 and isparallel with one of the side portions P4 of the support plate 650. Suchan embodiment accommodates insertion of the prosthetic joint 600 usingan oblique approach as opposed to the anterior, lateral, ortransforaminal approaches discussed above. In some embodiments, theposition of the keel 670 can be offset to help circumvent veins,arteries, bony portions, or other obstacles that may be in place duringthe insertion of the joint 600.

It should be further understood that other positions, shapes,orientations, and quantities of the keel 670 are also contemplated. Itshould also be understood that more keels 670 can be used, for similaror additional reasons. Also, the keel 670 may be angled, tapered, orconfigured in some other shape to facilitate the functional demands ofthe keel. In still another embodiment, the keel 670 may be configured asa winged keel, including a transverse portion (not shown) extendingacross the main body portion of keel 670.

In one embodiment, the keel 670 also includes a pair of openings 676extending therethrough to facilitate bone through-growth to enhancefixation to the adjacent vertebra. Additionally, a gap 678 may also beformed in the keel 670 to further facilitate bone through-growth. Thegap 678 also provides a reference point such that an X-ray can be usedto evaluate the positioning and alignment of the support plate 604during insertion of the prosthetic joint 600. It should be understoodthat any number of openings 676 or gaps 678 may be defined through, keel670, including a single opening or gap or several openings or gaps. Itshould also be understood that the openings 676 and gap 678 need notnecessarily extend entirely through the keel 670, but may alternativelyextend partially therethrough. It should further be understood that thekeel 670 need not necessarily define any openings 676 or gaps 678extending either partially or entirely therethrough. Additionally,although the openings 676 are illustrated as having a circularconfiguration, it should be understood that other sizes andconfigurations of openings 676 are also contemplated. As discussedabove, the surfaces of the articular component 602 that are in directcontact with vertebral bone are preferably coated with a bone-growthpromoting substance. Specifically, the bearing surface 654 and thesurfaces of the keel 670 can be coated with hydroxyapatite to promotebony engagement with the adjacent vertebrae. As also discussed above,the bearing surface 654 and the surfaces of keel 670 can be roughenedprior to application of the hydroxyapatite coating.

In some embodiments, one or both of the keels 640, 670 may include asharp forward edge, illustrated by edges 680, 682. By having such anedge, insertion of the keels 640, 670 into the associated vertebral bodyis facilitated. Also, the edges 680, 682 can be of sufficient sharpnessthat the vertebral body does not require a slot for receiving the keel640, 670, discussed in greater detail below.

Referring to FIGS. 42-44 a, to accommodate insertion of the prostheticjoint 600 within the intervertebral space, the upper and lower vertebraeV_(U), V_(L) can be prepared to accept the prosthetic joint 600therebetween. Referring specifically to FIG. 43, for the configurationof the prosthetic joint 600 of FIGS. 38-40, multiple slots 690, 692 areformed along the vertebral endplates of the lower vertebrae V_(L) andthe upper vertebrae V_(U), respectively. The slots 690, 692 can becreated by the keels 640, 670 themselves, or can be prepared beforehandby one or more of the methods discussed above. It can be seen from FIGS.42-44, that if one or more vessels 694 are obstructing a straightanterior approach, the oblique approach will allow for ananterior/lateral insertion. The implant 600 design also ensures asufficient contact surface for contacting the bony endplates of thevertebrae V_(U), V_(L).

Referring to FIG. 44 b, in one embodiment, the prosthetic joint 600 canbe inserted into the intervertebral space via instrumentation such asthe guide as disclosed in co-pending application U.S. Ser. No.10/430,473, which is herein incorporated by reference. In one example ofan insertion process for inserting the prosthetic joint 600, the midlineM of the vertebrae V_(U), V_(L) is located using imaging equipment and apin 695 is inserted into the upper vertebra V_(U) along the midline. Anoblique guide member 696 is then connected to the pin 695 via a flange697 and a handle (not shown) associated with the oblique guide member696 is then adjusted to a proper position. An oblique pin 698 of theoblique guide member 696 is then impacted into the upper vertebra V_(U)to fix the oblique guide member, thereby indicating the enteringreference point and the direction of implant insertion for theprosthetic joint 600. The guide (not shown) can then be used to implantthe prosthetic joint 600 into the intervertebral space from ananterior-oblique approach, the details of which are more fully discussedin co-pending application U.S. Ser. No. 10/430,473.

V. Mobile-Bearing Prosthetic Joint

In another embodiment, the above-described prosthetic joints can bemodified to provide for translational movement as well as rotationalmovement. For example, referring to FIGS. 45-47, a mobile-bearingprosthetic joint for anterior insertion is generally referred to byreference numeral 700. It is understood that the mobile-bearingprosthetic joint 700 is described with respect to anterior insertion forthe sake of clarity only, and therefore, a variety of insertiondirections are contemplated for the mobile-bearing prosthetic joint.

The prosthetic joint 700 extends generally along a longitudinal axis Land includes a first articular component 702 and a second articularcomponent 704. The articular components 702, 704 cooperate to form theprosthetic joint 700 which is sized and configured for dispositionwithin an intervertebral space between a pair of vertebral bodies, suchas an intervertebral space 51 between adjacent vertebral bodies V_(S),V_(I) (FIG. 48).

The prosthetic joint 700 provides relative pivotal and rotationalmovement between the adjacent vertebral bodies V_(S), V_(I) to maintainor restore motion substantially similar to the normal bio-mechanicalmotion provided by a natural intervertebral disc but with the addedelement of translational motion. More specifically, the articularcomponents 702, 704 are permitted to pivot relative to one another abouta number of axes, including lateral or side-to-side pivotal movementabout a longitudinal axis L and anterior-posterior pivotal movementabout a transverse axis T. It should be understood that in oneembodiment, the articular components 702, 704 are permitted to pivotrelative to one another about any axes that lies in a plane thatintersects longitudinal axis L and transverse axis T. Additionally, thearticular components 702, 704 are permitted to rotate relative to oneanother about a rotational axis R. In addition, the articular components702, 704 are permitted to translate relative to one another as will befurther described.

Although the articular components 702, 704 of prosthetic joint 700 maybe formed from a wide variety of materials, in one embodiment, thearticular components 702, 704 are formed of a cobalt-chrome-molybdenummetallic alloy (ASTM F-799 or F-75). However, in alternativeembodiments, the articular components 702, 704 may be formed of othermaterials such as titanium or stainless steel, a polymeric material suchas polyethylene, or any other biocompatible material that would beapparent to one of ordinary skill in the art. The surfaces of thearticular components 702, 704 that are positioned in direct contact withvertebral bone may be coated with a bone-growth promoting substance,such as, for example, a hydroxyapatite coating formed of calciumphosphate. Additionally, the surface of the articular components 702,704 that are positioned in direct contact with vertebral bone may beroughened prior to being coated with the bone-growth promoting substanceto further enhance bone on-growth. Such surface roughening may beaccomplished by way of, for example, acid etching, knurling, applicationof a bead coating, or other methods of roughening that would occur toone of ordinary skill in the art.

Articular component 702 includes a support plate 706 having an articularsurface 708 and an opposite bearing surface 710. Support plate 706 maybe sized and shaped to substantially correspond to the size and shape ofthe vertebral endplate of an adjacent vertebra. The support plate 706can include one or more notches 712 or other types of indicia forreceiving and engaging with a corresponding portion of a surgicalinstrument (not shown) to aid in the manipulation and insertion of thearticulating joint 700 within an intervertebral space between adjacentvertebrae. The surgical instrument (not shown) is preferably configuredto hold the articular components 702, 704 at a predetermined orientationand spatial relationship relative to one another during manipulation andinsertion of the articulating joint 700, and to release the articularcomponents 702, 704 once properly positioned between the adjacentvertebrae.

In one embodiment, and referring to FIGS. 49 a and 49 b, a recess 714 isformed in the articular surface 708. A circumferential edge 716 definingthe recess 714 along the articular surface 708 is in a concentricrelationship with a recess surface 718, yet has a smaller diameterrelative to the recess surface due to a diverging circular side 720(FIG. 48 b) of the recess 714. Although described with reference tohaving a circular shape, it is understood that the recess 714 may takeany number of shapes such as square, triangular, or rectangular shapes.

Referring to FIGS. 50 a and 50 b, the recess 714 (FIG. 49 b) is designedto receive a portion of a modular projection member 722. The projectionmember 722 includes a flange portion 724, which is shaped to correspondto the shape of the recess 714. As such, the flange portion 724 includesa diverging circumferential side 726, which terminates at asubstantially planar engagement surface 728. The engagement surface 728is adapted to engage the substantially planar recess surface 718 (FIG.49 b). It is understood, however, that although depicted as beingsubstantially planar, the engagement surface 728 and the recess surface718 may take any number of corresponding shapes. The diameter of theengagement surface 728 is smaller than the diameter of the recesssurface 718, thereby allowing translation of the modular projectionmember 722 relative to the articular component 702.

The remaining portion of the modular projection member 722 is defined bya projection 730 having a convex shape, which may be configured as aspherical-shaped ball (half of which is shown). It should be understoodthat other configurations of the projection 730 are also contemplated,such as, for example, cylindrical, elliptical or other arcuateconfigurations or possibly non-arcuate configurations. It should also beunderstood that the remaining portion of articular surface 708 may takeon planar or non-planar configurations, such as, for example, an angularor conical configuration extending about the projection 224.

In one embodiment, the convex articular surface of the projection 730 isinterrupted by a surface depression or cavity 732 extending along theprojection 730. In one embodiment, the surface depression 732 isconfigured as a groove. However, it should be understood that othertypes of surface depressions are also contemplated, including nodepression at all. One purpose of the groove 732 is to facilitate theremoval of matter disposed between abutting portions of the articularcomponents 702, 704. More specifically, the groove 732 may aid inclearing out matter such as, for example, particulate material, that isdisposed between the abutting articular surfaces of components 702, 704.

Referring to FIGS. 45 and 49 b, a flange member or keel 740 extends fromthe bearing surface 710 and is configured for disposition within apreformed opening in the adjacent vertebral endplate (such as V_(I) inFIG. 47). In one embodiment, the keel 740 extends perpendicularly fromthe bearing surface 710 and is approximately centrally located along thebearing surface 710. However, it should be understood that otherpositions and orientations of the keel 740 are also contemplated.

In one embodiment, the keel 740 extends along substantially the entirelength of the support plate 706. Such an embodiment would accommodateinsertion of the articulating joint 700 using an anterior approach.However, as discussed above, other approaches such as lateral,transforaminal, and anterior-oblique approaches are also contemplatedfor insertion of the prosthetic joint 700. In a further embodiment, thekeel 740 may be angled, tapered, or configured in some other shape tofacilitate the functional demands of the keel. In still anotherembodiment, the keel 740 may be configured as a winged keel, including atransverse portion (not shown) extending across the main body portion ofkeel 740.

The keel 740 also includes a pair of openings 742 extending therethroughto facilitate bone through-growth to enhance fixation to the adjacentvertebra. However, it should be understood that any number of openings742 may be defined through keel 740, including a single opening or threeor more openings. It should also be understood that the openings 742need not necessarily extend entirely through the keel 740, but mayalternatively extend partially therethrough. It should further beunderstood that the keel 740 need not necessarily define any openings742 extending either partially or entirely therethrough. Additionally,although the openings 742 are illustrated as having a circularconfiguration, it should be understood that other sizes andconfigurations of the openings 742 are also contemplated. As discussedabove, the surfaces of the articular component 702 that are in directcontact with vertebral bone are preferably coated with a bone-growthpromoting substance. Specifically, the bearing surface 710 and thesurfaces of the keel 740 can be coated with hydroxyapatite to promotebony engagement with the adjacent vertebrae. As also discussed above,the bearing surface 710 and the surfaces of keel 740 can be roughenedprior to application of the hydroxyapatite coating.

Referring to FIGS. 45-47, in one embodiment, the articular component 704includes a support plate 750 having an articular surface 752 and anopposite bearing surface 754. Support plate 750 may be sized and shapedto substantially correspond to the size and shape of the vertebralendplate of an adjacent vertebra. The support plate 750 can include oneor more notches 756 or other types of indicia for receiving and engagingwith a corresponding portion of a surgical instrument, such as discussedabove with reference to articular component 702.

In one embodiment, the articular surface 752 includes a recess 758 (FIG.47), which has a convex shape, such as that of a spherical-shapedsocket. However, it should be understood that other configurations ofthe recess 758 are also contemplated, such as, for example, cylindrical,elliptical or other arcuate configurations or possibly non-arcuateconfigurations. The remaining portion of the articular surface 752 canbe angled or otherwise configured to facilitate the insertion and/or useof the articulating joint 700.

Although the concave recess 758 is illustrated as having a generallysmooth, uninterrupted articular surface, it should be understood that asurface depression or cavity may be defined along a portion of therecess 758 to aid in clearing out matter, such as particulate debris,that is disposed between the abutting articular surfaces of articularcomponents 702, 704. In such case, the convex articular surface of theprojection 730 may alternatively define a generally smooth,uninterrupted articular surface. In another embodiment, each of theconvex projection 730 and the concave recess 758 may define a surfacedepression to facilitate removal of particulate matter disposed betweenthe abutting articular surfaces.

A flange member or keel 760, configured similar to the keel 740 ofarticular component 702, extends from the bearing surface 754. In oneembodiment, the keel 760 extends perpendicularly from the bearingsurface 754 and is approximately centrally located along bearing surface754. However, it should be understood, that other positions andorientations of the keel 760 are also contemplated. It should also beunderstood that the articular component 704 may include two or morekeels 760 extending from the bearing surface 754.

In one embodiment, the keel 760 extends along substantially the entirelength of the support plate 750. Such an embodiment would accommodateinsertion of the prosthetic joint 700 using an anterior approach.However, as discussed above, other approaches such as lateral,transforaminal, and anterior-oblique approaches are also contemplatedfor insertion of the prosthetic joint 700. In a further embodiment, thekeel 760 may be angled, tapered, or configured in some other shape tofacilitate the functional demands of the keel. In still anotherembodiment, the keel 760 may be configured as a winged keel, including atransverse portion (not shown) extending across the main body portion ofkeel 760.

The keel 760 also includes a pair of openings 762 extending therethroughto facilitate bone through-growth to, enhance fixation to the adjacentvertebra. However, it should be understood that any number of openings762 may be defined through keel 760, including a single opening or threeor more openings. It should also be understood that the openings 762need not necessarily extend entirely through the keel 760, but mayalternatively extend partially therethrough. It should further beunderstood that the keel 760 need not necessarily define any openings762 extending either partially or entirely therethrough. Additionally,although the openings 762 are illustrated as having a circularconfiguration, it should be understood that other sizes andconfigurations of openings 762 are also contemplated. As discussedabove, the surfaces of the articular component 704 that are in directcontact with vertebral bone are preferably coated with a bone-growthpromoting substance. Specifically, the bearing surface 754 and thesurfaces of the keel 760 can be coated with hydroxyapatite to promotebony engagement with the adjacent vertebrae. As also discussed above,the bearing surface 754 and the surfaces of keel 760 can be roughenedprior to application of the hydroxyapatite coating.

In some embodiments, one or both of the keels 740, 760 may include asharp forward edge, illustrated by edge 760 a of FIGS. 45 and 46. Byhaving such an edge, insertion of the keel 740, 760 into the associatedvertebral body is facilitated. Also, the edge 760 a can be of sufficientsharpness that the vertebral body does not require a slot for receivingthe keel 760, discussed in greater detail below.

Referring to FIG. 45, the mobile-bearing prosthetic joint 700 isassembled by inserting the modular projection 722 member into the recess714 formed in the articular surface 708 of articular component 702. Uponassemblage, the prosthetic joint 700 is ready to be inserted into thedisc space S1 between adjacent vertebral bodies V_(S), V_(I) (FIG. 48).

Referring to FIG. 48, to accommodate insertion of the prosthetic joint700 within the intervertebral space S1, the adjacent vertebral bodiesV_(S), V_(I) can be prepared to accept the prosthetic joint 700therebetween. For the configuration of the prosthetic joint 700 of FIGS.45-47, slots 770, 772 are formed along the vertebral endplates of thevertebrae V_(S) and the vertebrae V_(I), respectively. The slots 770,772 can be created by the keels 740, 760, themselves, or can be preparedbeforehand by one or more of the methods discussed above.

Upon insertion into the disc space S1, the prosthetic joint 700 allowstranslational movement of the articular component 704 relative to thearticular component 702 due to the engagement of the modular projection722 with the concave recess 758 of articular component 704. For example,in FIG. 51, the modular projection member 722 is shown in a posteriorposition (which would result in movement of the articular component 704in the posterior direction P), while in FIG. 52, the modular projectionmember 722 is shown in an anterior position (which would result inmovement of the articular component 704 in the anterior direction A).FIGS. 51 and 52 are of course only exemplary of the translationalmovement allowed by the implementation of modular projection member 722and the corresponding recess 714, and thus, the amount of translationalmovement of the modular projection member 722, and therefore thearticular component 704, relative to the articular component 702 canvary, including in directions other than P and A.

Furthermore, the positioning of the modular projection member 722 withinthe recess 714 of the articular component 702 allows the modularprojection to spin relative to the articular component 702. Thus, insuch an embodiment, the modular projection member 722 adds the benefitof being able to impart rotation to the articular component 704 (via theengagement with the recess 758) independent of translational movementimparted to the articular component 704. Such independent relationshipbetween translational and rotational movement adds to the amount ofmobility experienced at the prosthetic joint 700 relative to prostheticjoints for which translational movement is dependent upon rotationalmovement and vice versa.

The present disclosure has been described relative to several preferredembodiments. Improvements or modifications that become apparent topersons of ordinary skill in the art after reading this disclosure aredeemed within the spirit and scope of the application. For example, thearticulating components of the above-described articulating joints maybe reversed without departing from certain aspects of the disclosure.Accordingly, it is understood that several modifications, changes andsubstitutions are intended in the foregoing disclosure and, in someinstances, some features of the disclosure will be employed without acorresponding use of other features. It is also understood that allspatial references, such as “longitudinal” and “transverse,” are forillustrative purposes only and can be varied within the scope of thedisclosure. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the scope of thedisclosure.

1-39. (canceled)
 40. A spinal prosthetic device, comprising: a firstsupport plate having a first engagement surface for engaging a firstvertebra and a first articulation surface opposite the first engagementsurface; a first elongated keel member extending from the firstengagement surface, the first elongated keel member configured to engagea slot in the first vertebra; a second elongated keel member extendingfrom the first engagement surface spaced from the first elongated keelmember and in substantial alignment with the first elongated keel membersuch that the second elongated keel member is further configured toengage the slot in the first vertebra; and a second support plate havinga second engagement surface for engaging a second vertebra and a secondarticulation surface for articulatingly engaging the first engagementsurface of the first support plate.
 41. The spinal prosthetic device ofclaim 40, wherein a gap between the first elongated keel member and thesecond elongated keel member is defined by the space between a firstsurface of the first elongated keel member and a second surface of thesecond elongated keel member.
 42. The spinal prosthetic device of claim41, wherein the first surface of the first elongated keel member extendsperpendicular to the first engagement surface and the second surface ofthe second elongated keel member extends perpendicular to the firstengagement surface.
 43. The spinal prosthetic device of claim 42,wherein the first surface of the first elongated keel member extendsparallel to the second surface of the second elongated keel member. 44.The spinal prosthetic device of claim 42, wherein the first elongatedkeel member includes a first pair of side surfaces that extendsubstantially parallel to one another and the first surface of the firstelongated keel member extends between the first pair of side surfaces atan oblique angle.
 45. The spinal prosthetic device of claim 44, whereinthe second elongated keel member includes a second pair of side surfacesthat extend substantially parallel to one another and the second surfaceof the second elongated keel member extends between the second pair ofside surfaces at an oblique angle.
 46. The spinal prosthetic device ofclaim 45, wherein the first surface of the first elongated keel memberextends parallel to the second surface of the second elongated keelmember.
 47. The spinal prosthetic device of claim 41, wherein the firstsurface of the first elongated keel member extends at an oblique anglerelative to the first engagement surface and the second surface of thesecond elongated keel member extends at an oblique angle relative to thefirst engagement surface.
 48. The spinal prosthetic device of claim 47,wherein the first surface extends away from the second surface.
 49. Thespinal prosthetic device of claim 40 wherein each of the first andsecond elongated keel members have at least one hole extendingtherethrough.
 50. A spinal prosthetic device, comprising: a firstsupport plate having a first engagement surface for engaging a firstvertebra and a first articulation surface opposite the first engagementsurface; a first elongated keel structure extending from the firstengagement surface, the first elongated keel structure having a firstportion extending along a first direction and a second portion extendingalong the first direction in substantial alignment with the firstportion, the second portion being spaced from the first portion; asecond support plate having a second engagement surface for engaging asecond vertebra and a second articulation surface for articulatinglyengaging the first engagement surface of the first support plate; and asecond elongated keel structure extending from the second engagementsurface, the second elongated keel structure having a third portionextending along a second direction and a fourth portion extending alongthe second direction in substantial alignment with the third portion,the fourth portion being spaced from the third portion.
 51. The spinalprosthetic device of claim 50, wherein a gap between the first portionand the second portion is defined by the space between a first surfaceof the first portion and a second surface of the second portion.
 52. Thespinal prosthetic device of claim 51, wherein the first surface of thefirst portion extends perpendicular to the first engagement surface andthe second surface of the second portion extends perpendicular to thefirst engagement surface.
 53. The spinal prosthetic device of claim 52,wherein the first surface of the first portion extends parallel to thesecond surface of the second portion.
 54. The spinal prosthetic deviceof claim 52, wherein the first portion includes a first pair of sidesurfaces that extend substantially parallel to one another and the firstsurface of the first portion extends between the first pair of sidesurfaces at an oblique angle.
 55. The spinal prosthetic device of claim54, wherein the second portion includes a second pair of side surfacesthat extend substantially parallel to one another and the second surfaceof the second portion extends between the second pair of side surfacesat an oblique angle.
 56. The spinal prosthetic device of claim 55,wherein the first surface of the first portion extends parallel to thesecond surface of the second portion.
 57. The spinal prosthetic deviceof claim 51, wherein the first surface of the first portion extends atan oblique angle relative to the first engagement surface and the secondsurface of the second portion extends at an oblique angle relative tothe first engagement surface.
 58. The spinal prosthetic device of claim57, wherein the first surface extends away from the second surface. 59.The spinal prosthetic device of claim 53 wherein a gap between the thirdportion and the fourth portion is defined by the space between a thirdsurface of the third portion and a fourth surface of the fourth portion,the third surface extending perpendicular to the second engagementsurface and parallel to the fourth surface.